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LAMONT GEOLOGICAL OBSERVATORY (Columbia University) Palisades, New York
CABLE FAILURES IN THE GULF OF CORINTH:
A CASE HISTORY
By
Bruce C. Heezen, Maurice Ewing, and G. L. Johnson
Prepared for
The Bell Telephone Laboratories Murray Hill, New Jersey
July, 1960
LAMONT GEOLOGICAL OBSERVATORY (Columbia University) Palisades, New York
CABLE FAILURES IN THE GULF OF CORINTH:
A CASE HISTORY
By
Bruce C. Heezen, Maurice Ewing, and G. L. Johnson
Prepared for
The Bell Telephone Laboratories Murray Hill, New Jersey
July, 1960
TABLE OF CONTENTS
Page
ABSTRACT 1
PREFACE 3
INTRODUCTION 3
Acknowledgments 3
SUBMARINE TOPOGRAPHY 4
Physiographic Provinces 4
Continental Shelf 12
Continental Slope 12
Gulf Floor 25
Corinth Abyssal Plain 25
REGIONAL GEOLOGY 25
Geomagnetic Profiles 27
Seismicity 27
SEDIMENTS 31
Sediment Distribution and Physiographic Provinces 31
Continental Shelf 31
Continental Slope 31
Gulf Floor 34
Corinth Abyssal Plain 34
Distribution of Recent Sediments, Discussion 35
Probable Pre-Recent Sediments 35
PHYSICAL OCEANOGRAPHY AND WEATHER 38
Weather 38
Tides 39
Serial Oceanographic Observations 44
Radiocarbon 44
SUBMARINE CABLE FAILURES 51
Cable Repair Data 51
Geographical Distribution of Cable Failures 64
Trench Line Repairs at Patras 65
Repairs Near the Break at Patras 65
The Narrows and Western Entrance to the 65
Gulf of Corinth 65
Seaward of Mornos River 70
in
Table of Contents (Cont'd.)
Page
Axial Canyon - Western Gulf of Corinth 70
Continental Slope Seaward of Erineous River 71
Continental Slope and Plain Seaward of the
Meganitis River 71
Continental Slope Seaward of Kratis and
Krios Rivers 71
Continental Slope Seaward of the Avgo River 77
Continental Slope Seaward of the Dendron River 77
Continental Slope Seaward of the Sithas River 81
Continental Shelf and Slope East of Sithas River 81
Continental Shelf in Corinth Bay 87
Approaches to the Corinth Cable Landing 87
Trench Line Repairs: Corinth 87
Discussion of Gulf of Corinth Cable Failure 87
Damage by Human Activity 87
Shelf Failures 91
Failures in the Narrows 91
Gravitational Movements 91
Turbidity Currents and Slumps: Breakage of Cables 91
Turbidity Currents and Slumps: Burial of Cables 93
Cable Diversions 93
Earthquakes 93
Cable Failures off the Sithas River 93
CONCLUSIONS 97
BIBLIOGRAPHY 99
IV
Page Figures
1 Geographical location of the Gulf of Corinth,
Index map. 5
2 Track of Research Vessel Vema in the Gulf of
Corinth. 6
3 Bathymetric chart of the Gulf of Corinth. 7
4 Physiographic provinces of the Gulf of Corinth. 8
5 Echo sounding corrections for the Gulf of Corinth. 10
6 Location of PDR profiles and sediment cores. 11
7 Profiles in Krissaios Gulf. 13
8 Bathymetric sketch of the Krissaios Gulf. 14 /
9 Profiles in Andikiron Gulf. 15
10 Bathymetric sketch of the Andikiron Gulf. 16
11 Vroma Spur, Fonias Trough and Kala Spur. 17
12 Ind'ex chart for PDR profiles shown in
Figs. 13-18. 18
13 PDR profiles of the western continental slope
of the Gulf of Corinth. 19
14 PDR profiles of the eastern continental slope of
the Gulf of Corinth. 20
15 PDR profiles of the southern continental slope
of the Gulf of Corinth. 21
16 PDR profiles of the southern continental slope
of the Gulf of Corinth. 22
17 PDR profiles of the northern continental slope
of the Gulf of Corinth. 23
18 PDR profiles of the northern continental slope
of the Gulf of Corinth. 24
19 Regional surface geology of the Gulf of Corinth
area. 26
20 Geomagnetic profiles in the Gulf of Corinth. 30
21 Graphic logs of core lithology. 33
22 Graphic logs of varves in core V-10-29. 37
23 Graph of annual rainfall at Vostissa. 40
24 Average meteorological data for Patras area. 41
25 Average meteorological data for Vostissa area. 42
26 Long profile of River Sithas and Sithas submarine
canyon. 43
v
Figures Page
27 Thor serial hydrographic stations in the
Gulf of Corinth and Ionian Sea. 45
28 Index Chart showing location of Thor and Vema
hydrographic stations. 46
29 Bathythermograph profile of the Gulf of Corinth
and Ionian Sea. 47
30 Location of Vema hydrographic observations and
bathythermograph observations in the Gulf of
Corinth. 48
31 Vertical distribution of temperature, salinity
and oxygen in the Gulf of Corinth. 49
32 Location and dates of all breaks and faults in
cables 1, 2 and 3 between Corinth and Patras. 52
33 Cable repair ’’diagram sheet" (see Table IV). 59
34 Chart of repairs to cables 1 and 3. gQ
35 Cable ship grappling for cable. 02
36 Cable ship hauling in a fault. 02
37 Cable ship paying out new cable to final splice. 02
38 Component parts of a typical deep sea telegraph
cable. 03
39 Location of all cable failures and cable repairs
in Areas 5A, 5B and 6. 7g
40 Location of all cable failures and cable repairs
at the mouth of the Sithas River. gg
41 Seasonal distribution of tension breaks. 92
PLATES
Plate 1 Selected PDR profiles of the Gulf of Corinth 9
TABLES
Table Page
I Earthquakes in the Gulf of Corinth area. 28
II Sediment cores obtained by VEMA in the
Gulf of Corinth. 32
III C14/C12 ratios in Gulf of Corinth and
Mediterranean water samples. 50
IV Typical report of cable repair. 53
V Cable repairs at Patras and approaches to Patras. 66
VI Cable repairs in and near The Narrows. 67
VII Cable repairs in the western gulf. 68
VIII Cable repairs seaward of Erineous and
Maganitis Rivers. 72
IX Cable repairs seaward of Kratis and Krios Rivers. 74
X Cable repairs seaward of the Avgo River. 78
XI Cable repairs seaward of the Dendron River. 80
XII Cable repairs seaward of the Sithas River. 82
XIII Cable repairs - Sithas River to Corinth Bay. 84
XIV Cable repairs at Corinth. 88
vii
Digitized by the Internet Archive in 2020 with funding from
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ABSTRACT
The Gulf of Corinth is a narrow, 65 mile long, 470 fathom
trench, which lies between the Peloponnesus and the mainland of Greece.
The canyons of the steep southern continental slope lead from major river
mouths to coalescing subsea fans. A narrow abyssal plain occupies the
deepest part of the gulf.
Three telegraph cables were laid the length of the gulf and
maintained for over fifty years. Two of the cables lay on the continental
slope and one traversed the abyssal plain. The two cables on the continen¬
tal slope were broken frequently by turbidity currents originating at the
mouths of the major rivers. On the few occasions when cable repairs were
made to the cable which crosses the abyssal plain, the cable was found
buried.
Turbidity currents are the predominant mechanism contribut¬
ing to the mechanical failure of cables in the Gulf of Corinth. The
relatively high frequency of failures in the cables lying on the continental
slope parallel to its trench, as compared to the virtual absence of failures
in the cable laid on the abyssal plain, is of general significance when con¬
sidering the layout of future cable routes, regardless of whether these
routes are in deep fjords or in the deep sea.
PREFACE
Several cable failures have occurred in the past few years in
the Alaskan Archipelago. Failures off the Stikine River in the Ratz Harbor
to Midway section and those off the Katzehin River in the Midway Point to
Skagway section of the first Alaska telephone cable have an interesting
counterpart in the cable failures which have occurred in the
Grecian Archipelago. The following report on the Gulf of Corinth cable
failures should be of particular interest to those engaged in the maintenance
or extension of the Alaska cable system.
INTRODUCTION
The Gulf of Corinth is a narrow 470-fathom-deep, 65-mile-
long arm of the Mediterranean which separates the Peloponnesus Peninsula
from the mainland of Greece (Fig. 1). It is connected with the Ionian Sea
on its western endbya narrow one-mile-wide 30-fathom-deep strait. At
the eastern end of the gulf an artificial 72-foot-wide and 26-foot-deep
canal connects the Gulf of Corinth with the Aegean Sea.
Several sounding surveys were conducted by both the
British and Greek hydrographic departments between the years 1840 and
1935. A submarine cable was laid the length of the gulf in 1884. Investi¬
gations relative to repairs of this and two later cables have proven valuable
in understanding contemporary geologic processes occurring in the gulf
(Forster 1890). A study of the cable failure data kindly supplied by Cable
and Wireless Ltd. constitutes a major part of this paper. In 1910 the
Danish research vessel THOR took a serial hydrographic station in the
gulf (Nielson 1912). J. Y. Cousteau's ship CALYPSO ran a sounding line
through the gulf and took biological samples in 1955 (Blanc 1958). The
research vessel VEMA of the Lamont Geological Observatory conducted
a reconnaissance survey from 22-24 July 1956. This survey (Fig. 2)
included 350 miles of PDR soundings, total intensity magnetic measure¬
ments, 2 hydrographic stations, 3 bathythermograph observations,
2 large-volume water samples for radiocarbon analysis, and 7 piston cores.
Acknowledgments. The preparation of this report was sup¬
ported by the Bell Telephone Laboratories. The 1956 reconnaissance survey
of the Gulf of Corinth by the research vessel VEMA was supported by the
Office of Naval Research and the Bureau of Ships, U. S. Navy. The cable
failure data was supplied by Cable and Wireless, Ltd.
3
The reconnaissance survey of the gulf was conducted by
Maurice Ewing with the assistance of R. S. Gerard, M. Landisman,
C. Hubbard, A. Roberts and M. Talwani. VEMA was under the command
of the late Capt. F. S. Usher.
During the preparation of the report the writers were aided by
W. S. Broecker, R. Gerard, J. Hirshman, and Marie Tharp. David Ericson
advised on the sediments and identified the foraminifera. The radiocarbon
measurements were made by W. S. Broecker.
SUBMARINE TOPOGRAPHY
The bathymetric chart of the Gulf of Corinth (Fig. 3) and the
physiographic province chart (Fig. 4) are based on the PDR (Precision
Depth Recorder) soundings made by R. V. VEMA (Fig. 2), the spot depths
shown on the U. S. Navy Hydrographic Office chart number 3963, and
soundings by the cable repair ships. The VEMA PDR soundings were
corrected to true depths according to the values given by Matthews (1939)
[Area 50]. A graph of sound-velocity corrections for echo soundings in
Area 50 is shown in Fig. 5. Selected PDR profiles are shown in Plate 1
and indexed in Fig. 6.
The Gulf of Corinth can be roughly divided on the basis of
gross geography into: (1) the central basin, (2) the western arm,
(3) the eastern arm, and (4) the gulfs of the northern shelf. The entire
Gulf of Corinth is about 65 nautical miles long and 10 miles wide. The
western arm is about 20 miles long and 5 miles wide; the eastern arm is
a separate basin about 13 miles long and 8 miles wide. The two northern
gulfs are roughly equilateral triangles with sides of about 6 miles.
Physiographic Provinces
The physiographic provinces delineated in Fig. 4 are based
on a study of the morphology represented on the PDR echograms. The
division of a small land-locked arm of the sea into provinces similar to
the grand division of the major ocean basins may seem unjustified.
However, the shelf of the gulf is directly connected with the continental
shelf of the Gulf of Patras; the slope descending from the shelf break to
the gulf floor greatly resembles the continental slope, and the rise and
abyssal plain of the gulf floor also resemble ocean features. Although
4 I
Fig. 1 Geographical location of the Gulf of Corinth, index map.
5
TR
AC
K
OF
R V
VE
MA
6
Fig
. 2
Tra
ck o
f R
. V
. V
EM
A i
n t
he G
ulf o
f C
ori
nth
, 22
to
24 J
uly
1956.
.. o
7
Fig
. 3
Bath
ym
etr
ic c
hart
of
the G
ulf o
f C
ori
nth
.
o rO
CD fO
8
Fig
. 4
Physi
ogra
phic
pro
vin
ces
of
the G
ulf o
f C
ori
nth
.
SOUTH NORTH
9
Pla
te 1
Sele
cte
d P
DR p
rofi
les
in t
he G
ulf o
f C
ori
nth
.
Their g
eo
gra
ph
ical
locati
on i
s sh
ow
n o
n F
ig.
6.
Depth
s are
in n
om
inal
ech
o s
oundin
g f
ath
om
s (8
00 f
m/s
ec).
CO
RR
EC
TIO
NS
IN
FAT
HO
MS
Fig. 5
FATHOMS
Echo sounding corrections for the Gulf of Corinth.
Add correction to uncorrected echo sounding to obtain the
depth. Curve is based on Matthews (1939) for area 50 and
is for use only where assumed sounding velocity is
800 fathoms/second.
10
11
Fig
. 6
Lo
cati
on o
f P
DR
pro
file
s and s
ed
imen
t core
s.
PD
R p
rofi
les
repro
duced i
n P
late 1
.
minute in scale when compared to the grand features of the major ocean
basins, these features do greatly resemble their ocean counterparts in
form and in probable origin. Thus, with some reservations, we propose
a three-fold division of the gulf into continental shelf, continental slope and
gulf floor.
Continental Shelf. The continental shelf of the Gulf of Corinth
is generally a poorly developed feature less than a mile wide. In the
center third of the gulf, along the southern shore, the shelf rarely exceeds
l/4 mile in width and comprises but a mere notch in the larger mountain
slopes which drop from mountain crests over 2300 meters high to depths
of over 800 meters on the gulf floor. Along the northern side of the gulf
the shelf reaches its maximum development in the Gulfs of Krissaios and
Andikiron. The shelf break lies 6 miles off shore in the northern gulfs and
in the Bay of Corinth. The continental shelf of the Ionian Sea extends
through the narrows to the vicinity of the Mornos Delta in the western arm
of the gulf.
The shelf break ranges in depth from 15 to 120 fathoms. In
general, the narrower the shelf, the shallower the shelf break. Thus the
shallowest shelf break is found along the southern shore and the deepest
(120 fathoms) seaward of the northern gulfs. Shelf terraces are
represented in Figs. 7 and 9 (the profiles are indexed in Figs. 8 and 10).
The most prominent terraces are at 19 fathoms, 23-25 fathoms,
40-41 fathoms, 42-43 fathoms and 45-47 fathoms. The capes of Vroma
Island and Kala Island are carried beneath the gulf by the subsea spurs of
the same name (Figs. 4 and 11).
The weak development of the continental shelf is certainly a
good indication of the gulf's comparative youth.
Continental Slope. There is a strong contrast in the form of
the northern and southern continental slopes of the central basin. The
southern slope is steep and straight, devoid of major benches or breaks
in slope (Figs. 4 and 12-18). In contrast, the northern slope is broken by
several major benches and is complexly dissected. The declinity of the
southern slope ranges from 12° to 18°. The declinity on the northern
slope, in contrast, varies from 5° to 15°. The western arm of the gulf
is floored by a 200-fathom plateau which extends eastward as two benches
along the northern and southern continental slopes of the central basin.
These benches virtually disappear east of 22° 25'E. Below these benches
the continental slope (or marginal escarpment) continues to the gulf floor.
The eastern arm is floored by a 200-fathom Alkionidrion Basin and is
separated from the central basin by a 150-fathom sill near the Kala Islands.
12
o
13
Fig
. 7
Pro
file
s in t
he G
ulf o
f K
riss
aio
s.
Fig. 8 Bathymetric sketch of the Krissaios Gulf.
Krissaios Gulf after U. S. Hydrographic Office Chart 4092.
Profiles A, B, C and D shown in Fig. 7. Contour interval
20 meters (10. 9 fathoms) on land, and 10 fathoms in
Krissaios Gulf.
14
0 4,000 METERS ALL SOUNDINGS IN CORRECTED FATHOMS
I-1-1-1-1
0 I 2 MILES
Fig. 9 Profiles in the Gulf of Andikiron.
15
—H- 22*40'
22 40
126
44
KORINTHIAKOS K6LPOS
ANDfKIRON KOLPOS From o Greek survey in 1935
wilti oddiiiom to 1949
Contour inlervol 20 meters (opproximotely 65 feet) J
SCALE 1 50 000
230
Fig. 10 Bathymetric sketch of the Andikiron Gulf.
Andikiron Gulf after U. S. Hydrographic Office Chart 4092.
Profiles A, B and C are shown in Fig. 9. Contour interval
20 meters (10. 9 fathoms) on land, and 10 fathoms in
Andikiron Gulf.
16
Fig. 11 Vrdma Spur, Fonids Trough and Kald Spur.
Profiles are tracings of PDR profiles indexed on Fig. 12.
Depths are in nominal echo sounding fathoms (800 fm/sec).
17
18
Fig
. 12
Ind
ex c
hart
for
PD
R t
racin
gs
sho
wn i
n F
igs.
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Fig
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24
The southern continental slope is slightly indented by sub¬
marine canyons seaward of each of the major streams. The northern slope
is, in contrast, dominated by small-scale tectonic relief related to the
extension of the east-west faults of the mainland westward into the gulf.
However, some of the dissection of the northern slope may be related to
submarine canyons. The major troughs and spurs of the northern conti¬
nental slope are indicated and named on the physiographic province map
(Figs. 4 and 11).
Gulf Floor. The gulf floor is divided into two major
provinces: (1) the rise, and (2) the Corinth Abyssal Plain. On the south
the rise is dominated by the subsea fans of the major submarine canyons.
On the north side the rise is narrower and of more uniform width. On the
west end of the central basin the large Western Corinth Fan stretches out
from the mouth of the Mornos Canyon, which leads from the Delphic Plateau
to the Corinth Abyssal Plain. The rise generally ranges from 1:35 to 1:17
in gradient, which is steeper than the normal continental rise. The rise
has its greatest width about 3 miles in the region of the fans which
spread out from the mouths of the submarine canyons of the southern
streams. Along the base of the north slope it maintains a width of about
1 mile through the length of the central basin.
Corinth Abyssal Plain. The center of the central basin of the
Gulf of Corinth is occupied by the Corinth Abyssal Plain. An abyssal plain
is a broad flat area of the deepest portion of an ocean basin where the
gradient of the bottom does not exceed 1:1000. The gradients of the
Corinth Abyssal Plain range from about 1:1250 to 1:3000. The plain,
about 2-3/4 miles wide and 27 miles long, ranges in depth from 465 to
470 fathoms. The general character of the plain is well illustrated by the
profiles in Plate 1. In the western arm of the gulf an area of near-
abyssal-plain flatness forms a "perched plain" on the Delphic Plateau. In
the eastern arm the small Alkionidrion Basin may contain an abyssal
plain about 3-1/2 miles in diameter.
REGIONAL GEOLOGY
A portion of the 1954 Geological Map of Greece (Zachos 1954)
is reproduced in Fig. 19. The Pindos Mountains, which are part of the
Alpine belt, form the backbone of Greece. The Pindos are composed of a
hard core of granites and serpentines flanked with Cretaceous limestones.
25
SURFACE GEOLOGY OF GULF OF CORINTH AREA
» T
r JL
ALLUVIUM
TERTIARY SEDIMENTS; LARGELY CLASTICS
CRETACEOUS LIMESTONE
EOCENE to MIOCENE FLYSCH
UPPER CRET. to OLIGOCENE FLYSCH
TRIASSIC-LOWER CRET. SHALES
TRIASSIC AND JURASSIC LIMESTONE AND SHALE
TRIASSIC LIMESTONE AND DOLOMITE
SEMI-METAMORPHOSED SEDIMENTS
PRE-TERTIARY INTRUSIVES
from Zachot, 1954
SCALE* 1:500,000
Fig. 19 Regional surface geology of the Gulf of Corinth area.
Based on "Geologic Map of Greece” by the Institute for
Geology and Subsurface Research, Athens, 1954.
26
Geologists who have studied Greece believe that the folding of
the Pindos began in the late Cretaceous and continued into the Miocene
(Renz 1955; Brunn 1956). After the folding, they believe that the topography
of Greece was greatly altered by rifting and subsidence. The steep slopes
of the Gulf of Corinth suggest that the gulf originated through normal
faulting. Since the Pindos range at The Narrows is not displaced either
to the east or to the west, the faulting seems to have been dominantly
vertical. The Gulf of Corinth is generally believed to represent an
asymmetrical graben. Several other asymmetrical grabens cut across
the Pindos (Brunn 1956) but are not as deep as the Gulf of Corinth. In each
case the southern scarp is much steeper than the northern side.
Geomagnetic Profiles
A continuously recording total-intensity fluxgate magnetometer
was towed behind the R. V. VEMA during the reconnaissance survey of the
Gulf of Corinth. Three typical profiles across the Gulf of Corinth repro¬
duced in Fig. 20 show a general lack of large magnetic anomalies. This
general lack of magnetic anomalies over the steep slopes of the gulf is
surprising. However, this is not the first example of apparent large
faults failing to produce significant anomalies (Miller and Ewing 1956)
(Davidson and Miller 1955).
Seismicity
The most severe recent earthquakes in the Gulf of Corinth
area are listed in Table I. In addition, light quakes are common in the
area. The distribution of epicenters in central Greece shows an alignment
along the Gulf of Corinth. This alignment suggests that the major faults
which bound the Gulf of Corinth are still active.
The seven cable failures in the gulf cables which occurred
during or after earthquakes, were probably caused by slumps or
turbidity currents triggered by the earthquake shock (Heezen and
Ewing 1952, 1954).
27
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SEDIMENTS
Seven piston cores were obtained in the Gulf of Corinth with
a 1200-pound Lamont Geological Observatory piston corer (Heezen 1953).
The pertinent geographical data for the seven stations is listed in
Table II. The positions of the cores are indicated in Fig. 6 and their
lithologies are indicated in graphic form in Fig. 21.
Sediment Distribution and Physiographic Provinces
Continental Shelf. Bottom notations, although scarce on
H. O. charts 3963 and 4092, indicate sand, mud, shell sand, and stones
on the continental shelf. Such variety is characteristic of shelves
throughout the world. Core V-10-30 was the only core taken by VEMA
from the Gulf of Corinth continental shelf. This core, taken from the
44-fathom terrace in the center of the Krissaios Gulf, consisted mainly of
a firm white, highly-calcareous lutite throughout its length of 898 cm.
Several sand pockets are found in the first 25 cm. , a single one occurs
at 147 cm. and one sandy silt layer occurs at 378-386 cm.
Continental Slope. Chart notations on H. O. 3963 record
stones, mud, sand and rock from the continental slope. Two piston cores
were obtained from the continental slope. Core V-10-34, obtained in
219 fathoms, one mile northwest of Yerania Peninsula, consists of light
brown silty lutite. Pebbles of 2 cm. diameter occur near the top and
bottom. The bottom 78 cm. is disturbed in a manner which suggests
slumping. The shortness of the core (2. 4 m) implies that a firmer
stratum was reached which limited penetration.
Core V-10-29 was obtained from near the base of the conti¬
nental slope in 391 fathoms, 4-3/4 miles seaward of the Vouraikos River.
It consists of a 20 cm. layer of brown silty lutite over a 6 cm. bed of
gravel, which in turn overlies a 97 cm. varved sequence which extends to
the base of the core.
The steepness of the slopes, the shortness of the cores and
the frequent notations of rock and stones on the nautical chart support the
conclusion that most of the sediment deposited on the slope is removed by
gravity slides and turbidity currents. The varved sequence of
core V-10-29 is certainly pre-Recent in age.
31
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33
Fig
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Gra
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Gulf Floor. The sparse chart notations on H. O. 3963 record
mud and, on two occasions, sand from the gulf floor. Four cores were
obtained from the gulf floor. Core V-10-32 from the rise, 3 miles north
of the continental slope, consists of 188 cm. of light brown silty lutite with
one thin layer of greyish lutite. Si> disturbed zones suggest that slumping
from the adjacent continental slope had redeposited some of the sediments.
The absence of course detrital sediments or graded beds suggests that
turbidity currents were not involved. One small rounded piece of limestone
about 3 cm. in diameter was found at the top of the core.
Core V-10-28, obtained from a depth of 207 fathoms on the
Perched Plain of the western arm of the gulf near the Mornos Delta, con¬
sists of sand and silt interbedded with light brown silty lutite. Grading is
apparent in several beds. Pockets of sand and silt occur sporadically in
the lutite. The silts and sands are certainly deposits of turbidity
currents.
East of the Perched Plain a submarine canyon or trench
leads to the Western Corinth Fan. Core V-10-31 taken on the Western
Corinth Fan contains the thickest and coarsest sands found in any of the
cores from the gulf. Nearly half the core consists of sand. The beds are
consistently and obviously graded. In addition to these, there are several
silt layers with sand pockets and sand layers with silt pockets. In three
of the sandy layers there are bits of vegetable matter up to 0. 5 mm in
diameter.
Corinth Abyssal Plain. The only core raised from the
Corinth Abyssal Plain is V-10-33, obtained in 468 fathoms at the extreme
northeast edge of the plain. Since the predominant source of elastics
seems to be from the south and west, it is not too surprising that the
sands and silts are thin and make up less than 10% of the core. The
thickest of the beds of coarse sediment measures 8 cm. Much of the
lutite in this core may have been deposited by arrested turbidity currents
which had deposited their coarser loads nearer shore. A slump-contorted
zone in this core between 325 and 407 cm. depth may have resulted from
the same disturbance represented in cores V-10-32 and V-10-34. The
later cores were only about 7 miles to the southeast of Core V-10-33.
34
Distribution of Recent Sediments. Discussion. The pattern
of sediment distribution correlates well with the form of the submarine
relief. Unconsolidated sediments are thin on the continental slope. Those
unconsolidated sediments present are disturbed, and older sediments are
reached when even slightly greater penetration is achieved. Similar
results have been obtained in continental slopes throughout the world
(Heezen et al, 1959).
The rise appears to represent an accumulation of slump and
turbidity current deposits at the base of the continental slope. The
possibility that the northern and northeastern portions of the rise were
built up by slumping alone rather than deposition by turbidity currents, is
supported by core V-10-33, which, while containing no silts or sands,
displays slump-contorted lutites.
The somewhat speculative topographic identification in the
west part of the central basin of a depositional fan (Western Corinth Fan)
is supported by the thick graded sands found in Core V-10-31. Similar
thick beds found in Core V-10-28 at least suggest that the Perched Plain
as well as the Western Corinth Fan are fed from the west with significant
contributions from the Mornos River.
The abyssal plain core (V-10-33) supports the concept of a
turbidity-current origin of this physiographic feature. The thinness of
the beds in this core tentatively suggests a southwest or western source.
This in turn also suggests a dominantly nonturbidity-current origin of the
northern rise. Although no cores were obtained from the fans along the
south side of the gulf, cable repair work, to be described in a later
section of this paper, supports the dominantly turbidity-current origin of
these features.
Probable Pre-Recent Sediments. One of the most interesting
cores is V-10-29 from the continental slope north of Vouraikos River.
The top 20 cm. is composed of silty lutite containing a fairly rich marine
assemblage. Beneath is a 6 cm. layer of coarse, moderately rounded
gravel up to 1 cm. in diameter. The remainder of the core consists of
varve-like layers mostly 30 to 900 cm. in thickness. Foraminifera are
rare and may represent reworking, since several of them are identifiable
as pre-Pleistocene. Ostracods are common. Dr. L. Kornicker, who
examined the Ostracods from this core, reported (personal communication)
that the sample from 40 cm. depth:
35
. . produced about 11 shells belonging to 6 species. All ostracods present are of benthonic types. The thin shells of these ostracods, the dominance of smooth shelled forms over ornamented forms, the lack of intricate dentition on the shells suggest fresh water environment. The assemblage does not contain species restricted to marine waters nor does it resemble a random sample of ostracods from the marine environment. This leads me to believe the ostracods in the sample are from fresh, possible brackish (very low salinity, less than say 14o/oo) water. A brief survey of fresh water literature on hand led to tentative recognition of at least one species as a form restricted to fresh or brackish water. The high diversity of specimens (6 species in 11 specimens) indicates a large body of water, but I cannot estimate depth from this sample. M
The varyes vary in thickness from 5 to 4090 microns, with the
exception of one layer of 14, 600 microns (Fig. 22). The dark layers are
almost invariably of a reddish color and considerably thinner (5 to 1640)
than the light layers (30 to 4090) (Fig. 22). Pyrite is found tnroughout
the core and in places actually forms thin layers.
Seibold (1958) studied a modern varved sequence in cores
obtained from a shallow restricted marine embayment in the island of
Mljet off the Yugoslavia coast, 380 miles north of the Gulf of Corinth.
Seibold was .able to correlate variations of the thickness of the annual
varves with historical climatic cycles. In the Gulf of Corinth the dark
layers are thinner than the modern varves of Mljet (30 vs. 70 microns) and
the lighter varves, thicker (900 vs. 140 microns). The dark layers of the
Mljet varves are described as black and the light varves as white. The
Corinth varves consist of alternately reddish layers with light tan layers.
The varves at Mljet are being deposited beneath the
anaerobic waters of a shallow marine embayment. Those of the Gulf of
Corinth may represent a similar environment which may have existed
early in the history of the gulf. The pre-Pleistocene foraminifera found
in varves of Core V-10-29 may not have been displaced and may truly
indicate that the varves were laid down on the anaerobic bottom of a pre-
Pleistocene embayment.
It is generally believed that late Pleistocene sea level fell at
least 40 to 50 fathoms below the present level. The present sill depth of
the gulf is 30 fathoms and if neither tectonics or sedimentation have
significantly shallowed the sill, the gulf could have been cut off from the
Ionian Sea during the Pleistocene lows. The varved sequence could con¬
ceivably represent sedimentation during a Pleistocene sea level low.
36
Fig. 22 Graphic log of varvesin core V-10-29.
Graph of thickness in microns of varves in core V-10-29.
37
Regardless of the interpretation of the varves, their presence beneath only
20 cm. of recent sediments indicates that erosion has been active on the
continental slope in recent times.
Core V-10-30 from the continental shelf also contains beds
suggesting brackish or nonmarine conditions.
David Ericson (personal communication) reports that,
"The top sample contains shells of pteropods, fairly numerous marine
benthic species of foraminifera and rare planktonic species. From 50 cm.
to 250 cm. , only rare specimens of benthic foraminifera are present.
Among these is Streblus beccarii, a species frequently found in brackish
water.
"At 300 cm. the presence of Globigerina bulloides and
Globigerinoides rubra as well as echinoid spines and ophiuroid ossicles
indicates that conditions in the gulf were similar to those of the present.
"From 340-450 cm. planktonic foraminifera are absent,
although a few marine benthic foraminifera and echinoid spines are
present.
"From 500-650 cm. marine and brackish water forms are
wholly absent; however, ostracods and fragments of calcareous algae are
very abundant.
"From 700-850 cm. echinoid spines, marine benthic and a
few planktonic species of foraminifera are present.
"In the bottom sample (896 cm.) remains of marine organisms
are entirely absent. "
A general interpretation assuming continuous subaqueous
deposition suggests two periods preceding the present when conditions on
the shelf were much as they are today. However, during deposition of most
of the section, the gulf's connection with the Ionian Sea may have been more
restricted than it is now. However, this core, taken in the Krissaios Bay
along the North coast of the Gulf of Corinth in 44 fathoms, may not contain
a continuous unbroken record of sedimentation.
PHYSICAL OCEANOGRAPHY AND WEATHER
Weather. The following description is taken from the sailing
directions, (anon. 1931):
38
"During the summer the winds are usually light and variable,
with those from west and northwest most prevalent. Occasionally the wind
from northwest blows strongly and raises a considerable sea in the eastern
part of the gulf. During the night at this season, it is generally calm.
"In the western part of the gulf the prevailing wind is from the
northeast. It usually commences at sunrise and increases its force as the
entrance is approached, when it forms the 'Gulf Wind' of the Gulf of Patras.
During the summer, when there is often a fresh breeze in the middle of the
gulf, it is calm in the Gulf of Salona and Aspns Spitia Bay on the northern
shore.
"In the winter, winds from east southeast are most prevalent,
and are accompanied by a mild thick atmosphere and rain. "
The Gulf of Corinth region is arid, the southern shore
receiving only about 23 inches of rainfall per year. The northern side is
more arid. Figure 23 shows the average rainfall by month at Vostissa.
During the wet season from September to March, the maximum rainfall
in 24 days is about 2 inches. In October up to 3 inches of rain may fall
in one day. Figure 24 shows the weather data for the Patras area, and
Fig. 25 shows the weather data for the Vostissa area.
There are numerous mountain streams which flow into the
gulf from the surrounding mountains with steep gradients (e. g. , Fig. 26).
During the dry summer months these streams are reduced to hardly a
trickle; however, during heavy rainfalls tney become raging torrents. The
spring thaws in the mountains in March and April produce destructive
floods. Turbidity currents frequently triggered at the river mouths during
the floods account for many of the cable failures along the continental
slope.
Tides. "The tidal action in the gulf is small, but is regular
and well marked. The range at spring is a little over 2 feet. In the
narrows the current is tidal, turning with the time of high and low water
at Trisonia Island on the north shore; setting into the gulf while the water
is rising there and out when falling. At spring it attains a velocity of
2 knots in the narrows. The set and velocity both are much influenced by
the previaling wind if strong. As the gulf widens east of Drepano Point,
the current soon ceases to be felt, and in the middle there is no regular
current, but a slight drift is frequently set up by the prevailing wind.
There is often a marked setting close around the prominent capes on the
northern shore, caused by the tidal current setting out of the bays. "
(Anon., 1931.)
39
o H
RAINFALL IN INCHES
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Based on (H. O. 153) (1931).
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43
The narrows of the Gulf of Corinth are swept by tidal currents
which at the surface attain a maximum velocity of two knots. Although
Hydrographic Office Chart 3963 shows no bottom notations in The Narrows,
the reports of two cable repairs record "mud and rocks" in the vicinity.
Of the eleven cable failures in the narrows, eight occurred during the
winter months. It seems likely that severe winter storms may augment the
tidal currents and may thus account for this winter increase in the number
of cable breaks.
Serial Oceanographic Observations. In August 1910 the
Danish research vessel THOR made a serial hydrographic section con¬
sisting of 5 stations across the Ionian Sea, including one station in the
Gulf of Corinth (Figs. 27 and 28). In July 1956 VEMA occupied two
serial stations in the gulf and made 3 bathythermograph lowerings
(Figs. 28, 29, 30, 31). It is clear that with such meager data only the most
general conclusions are permissible.
Nielsen (1912), in his report on the hydrographic observa¬
tions, noted that in the gulf "the hydrographic conditions below 100 meters
are very different from those found in the Ionian Sea, both the tempera¬
ture and salinity being much lower. " He pointed out that the deep water in
the gulf is formed locally by convection during winter cooling. Since each
winter somewhat different minimum temperatures are reached, he pre¬
dicted that wide differences would be observed from year to year, a
prediction which seems fulfilled by a comparison of VEMA. and THOR
data. The THOR stations of 1910 (Figs. 27 and 28) show cooler water
temperatures and higher salinities in both the Gulf of Corinth and in the
Ionian Sea. The oxygen content of the 1910 THOR water samples was
considerably higher than those observed by VEMA in 1956. This
difference in oxygen could be related to the long-term depletion of oxygen
in the deep ocean noted by Worthington (1954), but more likely it merely
reflects differences in the winter temperatures and intensity of convec¬
tion. Pollock (1951), who found an appreciable year to year variation
in the salinity of the deeper waters of the Adriatic Sea, concluded that the
salinity variations likewise resulted from variations in annual convection,
which in turn were related to year to year variations in the prevailing
weather.
Radiocarbon. Two 100-gallon water samples were taken in the
Gulf of Corinth for radiocarbon assay. The surface sample and the bottom
sample had, within the limits of error, the same ratios. These
ratios, shown below were the lowest observed in the Mediterranean.
44
45
Fig
. 27
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TABLE III
Lat. Long. Depth c14/c12 Location
38°N 23°E 0 -4. 5 Gulf of Corinth
38°N 22°E 800 -4. 1 Gulf of Corinth
34°N 26°E 0 -0. 5 Levant Basin
34°N 27°E 2340 -4. 1 Levant Basin
37°N 21°E 4200 -3.4 Ionian Sea
37°N 19°E 3390 -1. 4 Ionian Sea
(Values expressed as % difference from average North Atlantic
surface water.)
The fact that top and bottom samples give the same C^/C*2
ratios is precisely what one would expect in light of the clear evidence of
local, probably annual, renewal of the bottom water. The great apparent
age of the gulf waters as compared to the Mediterranean water at com¬
parable and even greater depths is, however, surprising.
To explain this great apparent age, we might suppose that,
(1) the annual overturn is so fast that the deep water has not sufficient
time to become equilibrated with the atmosphere, (2) low-apparent-age
water is entering the gulf from the Ionian Sea, or (3) that inert carbon
from the surrounding limestone terrain is entering the gulf through the
streams and is diluting the gulf water.
The first alternative is ruled out, since surface and deep
water both have great apparent ages. The second suggestion is unlikely
in view of the small depth and small cross section of The Narrows and the
lack of any obvious source of old water in the Ionian Sea.
It is concluded that the inert carbon contained in the lime¬
stones surrounding the gulf is continually being washed into the gulf. This
inert carbon lowers the C^Vc^ ratio. Annual overturn maintains this
uniform apparent age from top to bottom. The limited exchange of water
through The Narrows helps to preserve this great apparent age by
isolating the Gulf of Corinth waters from the Ionian Sea.
50
The abundant evidence of frequent turbidity currents cited in
relation to cable failures and sediment distribution suggests that these
currents may contribute significantly to the dilution of the gulf waters with
dead carbon.
SUBMARINE CABLE FAILURES
From 1884 to 1939 three cables traversing the length of the
Gulf of Corinth (Fig. 32) were maintained by the Eastern Telegraph
Company, now a subsidiary of Cable and Wireless, Ltd.
The northernmost cable, #2, laid in May 1884, passes along
the northern side of The Narrows, directly down the continental slope,
and across the abyssal plain to the Bay of Corinth. Cable #1 passed
through the center of The Narrows and along the narrow continental rise
and lower continental slope of the south side of the gulf. The southern¬
most cable, #3, laid in 1901, ran along the continental slope and shelf
close to the south shore of the gulf. Of the three cables, #2 had the
fewest failures and for that reason is the only one of the cables still in
service. Cables #1 and #3, which failed in about equal numbers, were
not renewed after World War II.
Cable Repair Data
The routine involved in repairing cables and the form of the
ship report were established nearly a century ago and have remained
virtually unchanged to this day. The type of data which the oceanographer
or geologist finds in the cable report is nearly always the same except in
those fortunate instances when an interested engineer or officer notes
something which appears significant or anomalous. In shallow water the
ends of a broken cable are frequently recovered. In deeper water,
however, the end is more frequently abandoned than recovered. In such
instances, the cause of failure is inferred from the condition of the
picked up cable, which sometimes lay miles from the actual failure. To
help the reader comprehend the nature of the repair data and their
limitations, and to indicate the procedure of repair, the full report of a
report of a routine repair is transcribed in Table IV with accompanying
Figs. 33 and 34.
51
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52
TABLE IV
SYNOPSIS OF REPAIR TO
The Eastern Telegraph Company, Ltd. Corinth-Patras No. 1 Section C. S. "Levant''
Diagram No. 16
Description and Cause of Defect: Break Submarine Landslide
Depth of Water in Fathoms: Nature of Bottom: Distance of First Splice: Distance of Final Splice: Present Length of Cable:
265 mud & clay 15/13-12/13t 12/13-15/I3t
355 mud & clay from Corinth, from Patras,
16. 331 nauts. 53. 414 nauts. 77. 295 nauts.
DATES
Fault Observed: m. (local time) on unknown 19 Ship Left Piraeus: 11:20 a. m. TT Tt TT 9Ih' Dec." 1911 Arrived on Cable Ground: 7:40 a. m. tt
TT TT 10th Dec. 1921 Final Splice Slipped: Ground Cleared and Set
2:30 p. m. TT TT TT 14th Dec. 1921
on Course for Patras: 2: 33 p. m. tt TT T T 14th Dec. 1921 Arrived at Patras: 7:55 p. m. TT TT TT 14th Dec. 1921
SUMMARY OF CABLE LAID IN ON REPAIR
New Cable: Picked up Cable out of Stock: Picked up and Relaid on Repair:
7. 550 nauts. nil nil
TOTAL 7. 550 nauts.
H. Finnis Electrician
53
TABLE IV (Cont’d)
REPORT ON THE REPAIRS TO
PATRAS-CORINTH Nrs. 1 & 3 Secs.
by C. S. "Levant”
9/l4th December 1921
11:20 a. m.
Friday, 9th December/21
Left Piraeus for Corinth cable house to localize breaks in
Patras 1 & 3 sections.
4:40 p. m. Arrived off Corinth cable house.
Tests placed breaks in numbers 1 & 3 at 223 ohm and
218 ohms, respectively, from here. The ends which were not
clean were apparently buried.
5:00 p. m. Left for night's anchorage. 5:18 p. m. anchored near Corinth.
05:80 a. m.
07:40 a. m.
Saturday, 10th
Left for ground. 1 2
Arrived and down grapnel (S. P. G. and Rennie ) to hook
Patras #1 end. The northerly weather was very fresh.
09:00 a. m. Hooked cable and continued to pick up. 9:35 a. m. cable aboard
type Dt 12/13t.
09:50 a. m. Cut and spoke to Patras. We did not delay by testing now as
weather was very unfavorable.
09:55 a. m. Buoyed Patras end. Soundings 355 mud and clay. . 390 nautical
miles D 12/13 was recovered to break. (Break due to landslide.)
There was a lull in the weather, and advantage was now taken to
grapple for Patras 3 end.
11:20 a. m. Down grapnel (S. P.G. and Rennie) to hook Levant l's 1st splice
24/10/19.
12:30 p. m. Hooked cable and continued to pick up. 12:50 p. m. cable aboard
type Dy 16/13.
1:05 p. m. Cut and called Patras, but found end insulated in office. Patras
had been told in the morning to cease watch, as we had intended
to shelter. D. R. to Patas Office 2. 2 megs. abs.
54
TABLE IV (Cont'd.)
1:35 p. m.
2:44 p. m.
4:00 p. m.
6:55 p. m.
Buoyed Patras 3 end. Soundings 95 m.
Recovered to break 1. 207 nautical miles D 16/13, in poor and
damaged state, owing to debris from torrents. The break was
caused by the usual submarine landslide, originated by the
heavy torrents from mountain water-courses.
Set on for shelter at Corinth. Northerly weather very fresh.
Arrived.
Sunday, 11th
05:30 a. m. Left for ground. Northerly weather very fresh. On approach¬
ing ground, Weather was found quite unsuitable for operations,
so ship was set on course for Gulf of Salona.
10:00 a. m. Anchored off Itea.
Monday, 12th
06:00 a. m.
7:30 a. m.
7:45 a. m.
8:02 a. m.
8:05 a. m.
10:10 a. m.
10:30 a. m.
10:45 a. m.
11:25 a. m.
Left for ground. Weather somewhat moderated.
Light up cable buoy on Patras 1 end, and set on to grapple for
Corinth 1 end. At this position, off Xylocastron, the position
of No. 3 very uncertain. On account of this it was decided to
sweep for Corinth 1 end well to the east, clear of deposit from
torrents, and where the soundings are rather more uniform and
the cables further apart.
D. G. ^ (S. P.G. and Rennie).
Cleared grapnel, which had fouled bottom.
D. G. and commenced fresh drive further east.
Hooked cable and continued to pick up. Strain considerable.
Cable aboard Dt 12/13 (Chiltern's repair, May 1900) Corinth 1
end.
Cut and tested to Corinth:
D. R. 15 v. l'Zn. . 26 meg. C. .26 meg abs. C. R.
180. 8 ohms.
Buoyed Corinth 1 end. Soundings 265 mud and clay.
Original cable picked up west to break. Strain very consider¬
able.
3 Down grapnel.
55
TABLE IV (Cont'd.)
2:00 p. m.
2:30 p. m.
3:00 p. m.
3:55 p. m.
4:00 p. m.
5:45 p. m.
06:00 a. m.
07:50 a. m.
08:20 a. m.
8:40 a. m.
9:00 a. m.
9:25 a. m.
10:50 a. m.
11:00 a. m.
11:20 a. m.
11:50 a. m.
12:10 p. m.
1:30 p. m.
1:35 p. m.
2:40 p. m.
Monday, 12th
Recovered 3. 877 nts. D. when cable parted at kink, . 210 nt.
from break. Most of the picked up cable had been deeply silted
in mud, and was jagged and ruffled, and in some parts had been
suspended, as there were trees and masses of branches and
weed entangled about it.
Set on to place staff on Patras 3 end buoy.
Set on to grapple for Corinth 3 end, after attending to Patras 3
end buoy. 3:05 p.m. D. G. (S. P.G. and Rennie).
Picked up grapnel, having passed well over line of cable with
no sign of hook.
Left for shelter as northerly weather had become too fresh for
further operations.
Anchored near Corinth.
Tuesday, 13th
Left for ground. Weather very unsettled.
Arrived and stood by. Heavy rain and haze.
D. G. (S. P. G. and Rennie) to hook Corinth 3 end.
Grapnels foul of bottom.
Changed grapnel for round bottom.
D. G. (rd. btm. medium) to hook 1/2 mile further east.
Grapnel foul of bottom.
Cleared same and resumed drive working eastwards to get
away from water-courses.
H. C. and c. p. u. 11.35 cable aboard. Dt 12/p^ original '01.
Cut and tested to Corinth cable house.
D. R. 15 v. l'Zn. . 38 meg. C. . 28 meg abs. C. R.
196 ohms.
Passed ends for 1st joint and spliced to Corinth 3 end.
Completed 1st splice. 15/13-12/13t. Soundings 48 m.
Continued to pull out and picked up.
Recovered 1. 35 nt. D. to break (due to landslide). The picked
up cable was not in a good state and bore numerous signs of
the effects of the torrents.
56
TABLE IV (Cont'd.)
Tuesday, 13th
4:20 p. m. Reached Patras 3 end, having expended 2.330 nts. Dt. 15/13
100/100.
Tests to Patras: - D. R. 15 v. l'Zn. 6. 5 megs. C. 6. 7 megs
abs. C. R. 471. 5.
Tests to Corinth: through pulled out cable: 1
D. R.=l "normal" C. R.=l 221. 2 ohms.
4:30 p. m.
4:55 p. m.
Passed ends for final joint and splice.
Completed and slipped final splice 15/l3-p6/l3 soundings
95 m. B. T. 58. 5.
4:58 p. m.
7:00 p. m.
Set on for Corinth Bay.
Arrived and anchored.
5:00 a. m.
7:15 a. m.
Wednesday, 14th
Left for ground to splice on to Corinth 1 end.
Arrived and brought Corinth 1 end on board.
Tests to Corinth cable house "normal. "
9:25 a. m.
10:28 a. m.
Passed ends for 1st joint and splice.
Completed 1st splice 15/13-12/ 13t. Soundings 265 mud and
clay. B. T. 58. 5.
10:30 a. m.
12:50 p. m.
Continued to pick up cable.
Reached Patras 1 end, having expended 7. 550 nts. Dt 15/15
100/100.
Tests to Patras C. H. : -
D. R. 15 v. l'Zn. . 35 meg. C. 36 meg abs.
T. C. R.=l 549. 4 approximately.
Tests to Corinth through picked up cable:
D. R. "normal" C.R. 263 ohms.
1:18 p. m.
2:30 p. m.
Passed ends for final joint and splice.
Completed and slipped final splice 12/ 13t-15/l3 soundings
mud and clay.
2:33 p. m.
7:55 p. m.
Set on for Patras.
Arrived.
57
TABLE IV (Cont'd.)
NOTE:
The number 1 section was diverted to the northward as there
was space for this, but the number 3 was taken direct, as we did not feel
justified in expending more cable than necessary since ship's stock D was
intended for renewals to other sections.
We consider, however, that when cable is available and repairs
are necessitated in this vicinity, that extensive diversions to the numbers 1
and 3 sections should be effected and thus eliminate the frequent interrup¬
tions which are invariably caused by the torrents.
H. F. Barrett
Commander
H. Finnis
Electrician
58
sD
O Z
<D
s rt
GO
59
Fig
. 33
Cable r
epair d
iagra
m s
heet
for
Table I
V.
REPAIRS TO PATRAS-CORINTH SECTION NOS. 1 it 3 by C, S. LEVANT
13-14. 12. 21
No. 3
1st Spl Dt - 15/13 - Dt 12/ 13
S77W Pyrgo Ch Dome 1700 yds Eat. 38' 4. 4'N Long. 22* 39.5'E Sdg 48 m. cl. Laid in 2. 330 Dt 15/ 13
F. S. Dy 16/ 13 - Dt 15/ 13
C. Kepheli Avgo Pk 53* 50 Mr Koryphi 42* 40 Pyrgo Ch Dome S38E 2900 yds Lat. 38° 6. 0’N Long. 22'36.25'E Sdg 95 m. cl.
Cut out
D: 2.564 P. U. Lev I's laid in spl 24. 10. 19 Lev I's F.S. 24. 10. 19 Grapnels used - S. Pr H Rennie at F.S. Large R. B. at 1st spl
No. 1 1st spl Dt - 15/ 13 - Dt 12/ 13
C. Kephali Avgo Peak 45* 3£
Mt. Koryphi 20' 00 Lat. 38' 5. 0'N Long. 22' 39.5'E Sdg 265 m. cl. Pyrgo Church Dome S 84W
4800 yds Laid in 7. 550 Dt 15/ 13 Used large R. B. , SP St Rennie grapnels
F.S. Dt 12/ 13 - Dt 15/13
C. Kephali Avgo Peak 64' 40
Mr. Koryphi 57' 32 Lat. 38'7.5'N Long. 22' 35. 45’E Sdg 355 m. cl. Pyrgo Church Dome S 35 E
Cut out_
D. 4. 277 P. U. D. ■210 abd.
4. 487 Total All splices between and including Lev. I laid in spl 4. 9. 09 and Lev. I F. S. 4. 9. 09
H. J. Barrett Commander
Fig. 34 Chart of repairs to cables 1 and 3, 10 to 14 December 1921.
60
When trouble develops in a submarine cable, it is usually
possible to locate the fault or break by determining the electrical
resistance or capacitance of the cable between the testing point ashore and
the point of failure at sea. The navigator of the repair ship can then
proceed to the vicinity of the trouble and mark the area with a buoy. The
cable ship then commences to grapple for the cable (Fig. 35). When the
cable has been raised to the surface, test leads are attached and the
fault is localized. When it is determined that the cable is electrically
sound to one of the shore stations, that end is buoyed. The ship then
proceeds to recover the cable on the other side of the fault or break
(Fig. 36). This end is picked up until the tests indicate continuity and
satisfactory insulation to the cable house. The faulty cable is cut out and
new cable from the ship's tanks is spliced on. The cable ship then com¬
mences paying out the new cable toward the buoyed end, which, when it
is reached, it is taken aboard (Fig. 37). Final tests are taken in both
directions. If these tests are satisfactory, the final splice is completed.
The cable is then eased over the bow and drops to the ocean bottom.
The cause of failure reported in repair reports is generally
not more than a word or two based on the engineer's experience, and
unfortunately depends to a large degree on conventional cliches. We must
try to analyze the ship report and the reported cause in order to recon¬
struct the evidence which led the engineer or ship captain to his con¬
clusion. From this uneasy point we can reinterpret his evidence in the
light of available oceanographic data and present theory.
Cable failures are divided into faults and breaks. A break
is a complete interruption of the electrical circuit. A fault is short to
ground without complete interruption of the circuit. Often, faults are
left in the cable for some time before the cable is repaired if they are
not too serious. Breaks are almost always accredited to "tension. " If
the writer of the report does not believe in submarine landslides, he may
ascribe a tension break to "suspension" of the cable across a chasm.
Suspension can, of course, cause failure, but the correct identification of
suspension failures is not easy. If the depth is less than 500 fathoms and
fishermen are known to frequent the area, the break is ascribed to
"trawlers. " Generally there are other telltale indications of trawlers'
damage such as "mauling, " "saw cuts” and "axe cuts. " If an earthquake
was observed preceding a cable break, "seismic disturbance" is
generally entered in the report.
61
Fig. 35 Cable ship grappling for cable.
CABLE BUOYED FAULT
MARK BUOY
* SHIP
THE SHIP HAULS IN UP TO FAULT
BUOYED CABLE NEW CABLE SPLICED IN
MARK BUOY
• SHIP JOINT
Fig. 37 Cable ship paying out new cable to final splice.
62
THE
MPONENT PARTS OP A
EEP-SEA CABLE
Copper Corductor
GutCa Percha /nsu/ator
Brass Tape
Jute
Sheat/mg Hf/res
Outer Coyer mgs
oCJute /ora
Protectt/f Compound
Fig. 38 Component parts of a typical deep sea telegraph cable.
63
Faults are generally ascribed to "chafe, " "corrosion, "
"chafe and corrosion, " "kink, " "deterioration, " "perished core, " "teredo,'
or "trawler maul. " If the armor wires are worn or bright, the failure is
ascribed to "chafe. " If the cable armor is corroded and not particularly
polished, the failure is ascribed to "corrosion. " If corrosion and
abrasion of the cable are observed in the picked up cable, "chafe and
corrosion" are reported. "Kink" or "tightened kink" is probably indicative
of tension insufficient to break the cable. However, it is often thought
that corrosion of a kink left in the original cable is involved and that no
additional tension is indicated. Frequently it is supposed that suspension
of an original kink over a long period of time has led to a particular
failure. "Deterioration" and "perished core" are probably indications of
bacterial action and "teredo, ” of course, refers to damage by this boring
isopod. Considering that the fault or broken end is frequently not
recovered and that the men writing the reports are generally not trained in
biology or geology, one realizes that he cannot take the brief one-or-two-
word reported cause in any specific report as more than an indication of
the condition of the picked up cable.
Frequently, however, exceptional observations are reported
more fully in the cable report and give us firmer ground. Some cable
engineers and captains, endowed with an exceptional interest in the cause
of failure and with a flair for writing, have furnished lights to guide us
through the fog. Figure 38 shows the component parts of a deep sea
cable.
Geographical Distribution of Cable Failures
The breaks and faults in the three Patras-Corinth cables are
summarized in Tables V-XIV from the data of laying to about 1957. At
that time only cable #2 was operating, #1 and #3 having been abandoned
during World War II.
Year Year Laid Records Cease
Cable #1 1884 1939
Cable #2 May 1889 1957
Cable #3 1901 1939
The data are grouped into ten areas and the failures are
listed chronologically for each area.
64
Trench line repairs at Patras, Area 1A. (See Table V and
Fig. 32.) All repairs listed for Area 1A are routine land renewals and
are of no oceanographic interest.
Repairs near the beach at Patras, Area IB. (See Table V
and Fig. 32.) Five of the seven repairs were due to natural causes, two
were due to anchor damage. The failures are too few in number to allow
the determination of significant patterns.
The Narrows and Western Entrance of the Gulf of Corinth,
Area 1C. (See Table VI and Fig. 32) Of the 14 failures, three can be
excluded as not being caused by the forces of nature. The cable repairs
made 66 to 72 nautical miles from Corinth lie in the western entrance,
and those 66 to 63 nautical miles are in The Narrows. Except for one
failure which was repaired 2/7/31 (date of failure unknown) and one which
occurred in August 1927, the remaining five failures occurred during the
normally stormy autumn and winter months.
The failures at the entrance show a similar pattern with
one repair in July (date of failure unknown) and 3 in the winter months.
These failures can be ascribed to chafe due to bottom cur¬
rents flowing through The Narrows. The specific times of failure may
have been determined by the occurrence of a particularly violent intensi¬
fication of the current which snapped the already chafed and weakened
cable. The high frequency of failures in the winter and autumn months
may be due to storm-augmented tidal current. It could also indicate
a particularly high westward flow of water along the bottom of the
straits. This may correspond with the formation of bottom waters by
the cooling and sinking of surface waters during the winter months. The
inward flow of surface water at the straits could at that time be balanced
by an outward flow along the floor of The Narrows. There are small
streams emptying into The Narrows which could occasionally cause
turbidity-current damage. The break on 21/2/21 has the appearance of
a turbidity-current failure, although it is impossible to be sure. The
Mornos River might also occasionally create a turbidity current in a
westward direction.
65
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69
Seaward of Mornos River, Area 2. (See Table VII and
Fig. 32.) Five of the six failures off the Mornos River were probably
caused by turbidity currents. The first break on 25/8/89 followed an
earthquake and was probably caused by a seismically triggered turbidity
current. (The same earthquake also caused a break in Area 5A.) The
fact that cables 1 and 3 which lie along the south shore of the strait did
not break in Area 2 supports the conclusion that all five breaks were due
to turbidity currents flowing down slope from near the mouth of the
Mornos River.
Just conceivably, the breaks in Area 2 may be due to the
outflow of deep gulf water along the bottom. A westward flow would be
deflected to the right, thus explaining the distribution of failures on the
right side only. However, the evidence seems to favor turbidity currents
from the Mornos River. Of course there may be a relation between the
frequency of turbidity currents off the Mornos River and the quantity of
sediment transported through the straits by the bottom current. The
rains in January-March may provide "teeth" to the bottom currents in the
form of detrital sediment, and the increased transport of sediment might
then cause the failures in The Narrows. Needless to say, this relation¬
ship is extremely speculative.
Axial Canyon - Western Gulf of Corinth, Area 3A. (See
Table VII and Fig. 32.) Three failures have occurred in cable 2 where
it crosses the Mornos submarine canyon, which runs from the vicinity
of the Mornos River mouth to the abyssal plain of the Eastern Gulf. The
failure in 1902 was probably caused by a turbidity current triggered by
a strong earthquake. This turbidity current probably originated near
the Mornos River and flowed down the canyon to the abyssal plain. Only
cable 2 was disturbed in this area because the other two cables do not
cross the Mornos Canyon. The canyon can be clearly seen in Fig. 3.
70
Continental Slope Seaward of Erineous River, Area 3B.
(See Table VIII and Fig. 32.) Four failures have occurred in this area.
In 1907 cables #1 and #3 failed on the same day. Both cables showed
evidence of violent strain. The two 1907 breaks could have been caused
by two currents, one flowing northwest and the other southeast, each of
which broke one cable without breaking the other. The concept of a
single large flow is, however, favored. Of the other failures, two were
in April and one in November, which corresponds generally to the time
of maximum precipitation, and are therefore probably the result of
turbidity currents generated by the Erineous River.
Continental Slope and Plain Seaward of the Meganitis River,
Area 4. (See Table VIII and Fig. 32.) The break on 9/11/1888 is
unrelated to the other three failures in this area. This break occurred
following the earthquake at 1704 L. S. T. 9/11/1888. The town of
Vostissa was destroyed and a moderate tsunami was observed on the
opposite side of the gulf. The town had been previously damaged in 1861
by an earthquake. It is presumed that most of the unstable sediment was
dislodged by these two earthquakes and for this reason, failures have
subsequently ceased in this area. There is some suggestion that the
20/11/88 failure in Area 5A may have actually occurred on the ninth,
having been triggered by the same earthquake. Of the remaining three
breaks in Area 4, two are on the abyssal plain of the gulf. Two were
faults and one was unrecovered.
Continental Slope Seaward of Kratis and Krios Rivers,
Area 5A. (See Table IX and Figs. 32 and 39.) There have been
12 failures in this area of which 7 can be definitely attributed to turbidity
currents and slumps. As can be seen from Fig. 3 there is a suggestion
of submarine canyons in this region, but unfortunately we have no echo-
grams in this area. It is difficult to ascertain if these breaks occurred /
in one large canyon fed by the Kratis, in several smaller individual ones,
or in several small canyons which join at the base of the slope to form one
larger canyon. It seems most likely that the Kratis, Peloponnesus, and
Krios have formed individual canyons which may join at the base of the
slope.
During the 1935 repair a jumble of debris was found tangled
in the cable. This break occurred along with several others during the
severe gales of December 1935. Of the four nontension breaks, it is
interesting to note that in two cases the cable was deeply buried, probably
by deposits of alluvium laid down turbidity currents and slumps.
71
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Fig
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Lo
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A,
5B a
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Continental Slope Seaward of the Avgo River, Area 5B. (See
Table X and Figs. 32 and 39.) There have been eight failures in this area.
Seven are clearly due to turbidity currents or slumping. The fault re¬
paired on 3/11/13 is most likely related in cause to the other seven. All
these failures occurred from September to February, which corresponds
well with the maximum precipitation (Fig. 23). The failures are aligned
in a NW and SW pattern along one large canyon. At 1630 L. M. T. on the
18th of September 1910, both cables 1 and 3 were broken. They must have
been broken by one large flow down the axis of the canyon. On all other
occasions, however, only one of the two cables broke. Cable #3, which
lay closer to the mouth of the Avgo, failed five more times, but
cable #1 failed only once again, during the December 1935 storms.
Cable #3 possibly escaped injury in 1935 because it was newer and there¬
fore stronger than the #1 cable, but it may have been buried; or lacking
obstructions or brush entanglements, the flow could have swept over it
without breaking it.
Continental Slope Seaward of the Dendron River, Area 6.
(See Table X3 and Figs. 32 and 39.) The eight failures in this area were
all the result of slumps or turbidity currents originating at the mouth of
the Dendron River. Cable #3 crosses the submarine canyon on the con¬
tinental slope, cable #1 lies at the base of the continental slope on the
narrow continental rise, and cable #2 lies on the abyssal plain. In 1908
three failures occurred in cable #3. In 1914 a fault developed in cable #2.
When repairing this fault, the repair ship found #2 deeply buried. They
parted the cable 18 times and finally had to abandon 12 nautical miles,
since they were unable to pick it up. It appears that the flows from 1884
until 1914 had deposited sufficient sediment over #2 to cause this difficulty.
These flows were either the ones which broke cable #3 in 1908, or else
smaller flows which did not have sufficient power to break any of the
cables. #1 was unaffected during this period, probably because it had
been buried by earlier flows. At 0430 L. M. T. 18 December 1920, both
#1 and #3 were broken. This was most likely the result of a single
large flow which had sufficient force to uncover and break #1 in addition
to #3. In 1935 #3 broke during the severe gale, which resulted in several
other failures. #1 was not affected in 1935 but in 1938 it was broken by a
turbidity current which deposited twigs and foliage in the area.
77
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Continental Slope Seaward of the Sithas River, Area 7.
(See Table XII and Figs. 32 and 40.) The nine failures in this area all
resulted from turbidity currents or slumps originating from the mouth of
the River Sithas (Fig. 40). The failures in cables #1 and #3 all occurred
in the submarine canyon of the River Sithas. In Fig. 16 canyons are visible
in profile 12S at shallow depth and again in profiles 11S and 12S at the base
of the slope. The one fault in #2 occurred in the abyssal plain. The
failures must have been caused by small turbidity currents because in
only one case (1921) did the #1 and #3 cables fail simultaneously. Although
#1 failed in 1904, 1909, 1914 and 1918 during the same interval, cable #3
did not fail once. The failures are probably to be attributed to small
turbidity currents which had enough force to break cables only on the
steepest slopes when they were traveling at their maximum velocity and
carried their maximum loads. The frequent reports of brush and tree
trunks suggests that only when they are carrying such debris, or when
enough is caught in the cables to present a sufficient obstacle, can the
currents exert enough pressure on the cables to cause failure.
This pattern is understandable if we consider the steep slopes
involved (Fig. 26), the frequency of trigger effects (earthquakes and floods),
and the consequently relatively small quantity of sediment available for
each flow. All the failures occurred in the autumn to winter months, again
possibly indicating a correlation between river discharge and failures.
Continental Shelf and Slope East of Sithas River, Area 8.
(See Table XIII and Fig. 32.) Of the five repairs reported for this
area, three are faults. Two repairs were made to cable #3, which lies
near the edge of the continental shelf in this area. The three repairs to
cable #1, which lies on the continental slope, may be due to slumps or
weak turbidity currents. Three of the failures occurred in March and
one in August. This suggests a possible correlation with the late winter
gales which may trigger displacements from the shore. The one failure
in April was due to a landslide triggered by an earthquake.
81
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85
AREA 7 CONTINENTAL SLOPE OFF MOUTH OF SITHAS RIVER
22- 35' 36' 37* 38' 39' 40'
CABLE NO I o
CABLE NO . 2 □ CABLE NO.3 A SOLID COLOR INDICATES FAILURE DUE TO TENSION SLANTED NUMERALS ARE SPLICE DEPTHS VERTICAL NUMERALS ARE VEMA SOUNDINGS
ALL DEPTHS IN CORRECTED FATHOMS
Fig. 40 Location of all cable failures and cable repairs at the mouth
of the Sithas River.
86
Continental Shelf in Corinth Bay, Area 9. (See Table XIII
and Fig. 32.) The seven failures in Corinth Bay all occurred between late
December and mid March. They are all (except possibly 26/12/39)
probably due to chafe, and their times of failure probably are determined
by the occurrence of heavy winter gales. Six of the seven failures were
breaks, which suggests that a strong current or slide caused the failures.
Since six of the failures were on the broad shelf of the Bay of Corinth, the
failures were probably due to the action of bottom currents on the cables
weakened by chafe rather than by slumps or turbidity currents.
Approaches to the Corinth Cable Landing, Area 10A.
(See Table XIV and Fig. 32.) Of the 22 failures near the beach at the
Corinth landing, all can probably either be attributed to anchors or other
human damage. The large number of ships that have hooked the cable
while waiting to clear the canal have necessitated such frequent repairs
to the cable that the wearing action of waves and currents have never had time
to chafe through any of the cables.
Trench Line Repairs, Corinth, Area 10B. (See Table XIV
and Fig. 32.) Trench line repairs due to deterioration have been less
frequent at Corinth than at Patras, since on several occasions ships have
pulled the cable out from the cable hut, requiring the replacement of the
entire shore end and trench line. The trench line cables and the cable used
in approach to the cable landings are usually B type. The remainder of the
cable length was almost invariably a form of D cable. This makes it
difficult to say that one cable broke and the other was unaffected because it
was a stronger type. It is most likely that if a type B or C cable had been
used to traverse the length of the Gulf of Corinth, the number of failures
would have been reduced significantly.
Discussion of Gulf of Corinth Cable Failures
Damage by Human Activity. Twenty-five failures have occurred
due to anchor damage. The great majority of these failures occurred off
Corinth, presumably inflicted by ships waiting to enter the canal. In two
cases the cable was stolen by robbers, and was once broken by fishermen's
dynamite. There are also two instances in The Narrows when boom defense
moorings damaged the cable. These failures have no geologic interest except
insofar as they make impossible a study of chafe due to breakers and surf.
87
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90
Shelf Failures. The 21 cable failures (excluding Area 2) on
the shelves ranging from 25-100 fathoms depth testifies that sufficient
abrasion occurs in those depths that the light (D) and intermediate (B) type
armoring is gradually worn through. The failures on the shelves cannot,
in general, be ascribed to gravitational movements, since the slopes are
too low to initiate movements and also too low to sustain them.
Failures in The Narrows. The cables pass through the
narrow straits known as The Narrows. Strong tidal currents flow in and
out through these straits at the surface. The depth of the sill is 30 fathoms.
The cables through The Narrows have broken seven times, generally in the
stormy autumn and winter months when gales might be expected to augment
the tidal action.
Gravitational Movements. The cables have been broken by
slumps and turbidity currents which originated off the mouths of rivers
emptying into the gulf. A minimum of 47 breaks have occurred which are
related to at least 10 different streams.
A most important conclusion of this study is that a turbidity
current may cross a cable without snapping it. The basis for this conclu¬
sion is that on only four occasions have both cables crossing a canyon
been broken simultaneously. On all other occasions either #1 or #3 failed
and the other one remained intact. Cable #2, which lies in the abyssal
plain, was found deeply buried during the very few times it was recovered.
The frequent reports of entanglements of brush and trees in the cables
indicates that the turbidity currents in the gulf generally do not break the
cables unless sufficient resistance is offered due to entanglements of
brush which increased the cable's effective cross section.
Turbidity currents and slumps; breakage of cables. There
are many mountain streams which empty into the Gulf of Corinth, and
during times of flood these streams carry a heavy load of sediment and
debris. As one can see from examining Tables V-XIV, there are many
cases in which branches, twigs and brushwood of various kind have been
found wrapped around the broken cable. As can be seen from Fig. 41,
there is a tendency for cable failures due to turbidity currents or slumps
to occur during the winter months, with November, December, and
January as the peak months. The high incidence of winter breaks corre¬
sponds to the season of maximum precipitation for the area (Fig. 23).
The December 1935 breaks occurred during the first heavy winter gales.
The repair ship log also notes: "Several torrents and one mountain
river debouch in the gulf in the immediate vicinity carrying, especially
91
Fig. 41 Seasonal distribution of tension breaks.
92
during the winter gales of rain and hail, a vast quantity of alluvium into
the sea. " In all, the cable ship repair logs list a total of 28 breaks as
due to submarine displacement or tension.
Turbidity currents and slumps; burial of cables. In the few
times that cable #2 developed faults, it was found to be buried. The fault
in Area 5A (Fig. 32) 5/19/49 could not be recovered, indicating deep
burial. Again in Area 6 - on 14/2/14 - the fault was unrecovered. The
repair ship had trouble raising the cable - a fact indicative of deep burial.
The cable was hooked and parted 18 times. The 7/4/09 break also showed
indications of burial.
Cable diversions. The cable company soon began to detour
its repairs in a loop around the areas where breakage was most frequent.
In Fig. 39 the 1935, 1937, and 1938 repairs on cable #1 represent
successful detours around the river mouths. The 1911 diversion for
cable #3 in Area 5B around Avgo River was not sufficiently far out and the
cable broke again in 1923. The 1914 diversion of cable #3 in Area 5A was
successful.
Earthquakes. There are at least 6 breaks which are
definitely associated with earthquakes. The earthquakes trigger slumps
along the slopes, which deeply bury and break cables in their path.
Following the 1889 August 25 earthquake which damaged Xilokastrom,
both #1 and #2 cables broke at widely separate areas.
Cable failures off the Sithas River - an example. The group
of cable failures located off the town of Xilokastron on the south shore of
the Gulf of Corinth is particularly interesting and will be discussed in
more detail (Fig. 40). In this immediate vicinity the River Sithas
empties into the gulf from the mountain Killini Seria, 2376 m. in
altitude (see Fig. 26). There have been nine cable failures here since
1904, six of which are definitely attributable to turbidity currents generated
at the mouth of the Sithas. With the exception of the break on
28 August 1909 (which probably was related to an earthquake), all the
breaks occurred during the autumn-winter season, which corresponds to
the time of maximum precipitation for this area. It seems probable that
the Sithas during times of flood, while swollen with silt and debris,
triggered the turbidity currents which caused the breaks.
We will examine the breaks in chronological order:
The first failure in this area occurred on 6 January 1904.
There is not much information in the repair ship's log book as to the dif¬
ficulties encountered in recovery. There is, however, one very significant
paragraph:
93
"The break in the cable was caused by heavy brushwood and
tree trunks from mountain torrents having been swept down and encircling
the cables, which must have been suspended between rocks, for the
circumference of the brushwood was five fathoms. "
The brushwood was almost certainly carried down the slope
by a turbidity current. It would appear in this case that the cable crossed
a submarine canyon scoured by turbidity currents. During the periodic
flooding of the river, material was swept down the submarine canyon with
some of it entangling in the cable. Eventually the mass of debris
increased to a point where its cross section offered such an obstruction
to turbidity currents that the cable snapped. Alternatively, the debris
could all have been carried by one large flow. In any case, a tangle of
brushwood thirty feet in circumference would no doubt offer sufficient
resistance to a turbidity current to break the cable.
The next break occurred 28 August 1909. This break was
probably related to an earthquake. Malladra (1925) lists this break as
"Seismic disturbances probably caused by landslide of a heavy mass of
hard clay on cable. " Obviously the landslide did not cause the earthquake,
but rather it seems likely that a small earthquake jarred loose some
alluvial sediment from the shelf. Since only cable #1 was broken, the
slump was either fairly small or originated seaward of cable #3 on the
continental slope, or else it passed over cable #3 without breaking it. It
would be expected that a slump would deeply bury that cable. The following
quotation from the ship's log will indicate the difficulties caused by this
deep burial:
"Grappled until 2 P. M. having made nine steady and long
sweeps over line of cable with no signs of having hooked it. Occasionally
the hard patches of clay were encountered and these 'brought up' the ship,
but the greater part of grappling ground appeared to be muddy and of a
viscous nature. "
(Next day) "Down grapnel. Ship made 7 drives, sweeping
carefully across line each time, and working gradually eastward
0. 75 naut. of cable had been covered but no signs whatever of having
hooked or touched it. It seemed very evident that the cable in this vicinity
was considrably embedded, for its true position was known and yet our
long prong grapnel could not reach it. "
(Following day) "After nine drives and when ship had gradually
worked eastwards to . 45 nauts. east of Levant #1 (first splice March 04),
the cable was hooked. Commenced to pick up cable bight.
94
"A very heavy strain was soon observed, however, and when
the cable had been raised about 150 fathoms from bottom, the picking up
of gear could not overcome the strain. Occasionally the strain would give
way for a moment, and a few fathoms of rope could be snatched. But this
state of affairs did not last long, for at 2 P. M. the strain fell suddenly,
indicating the cable had parted to the westward.
’’Hooked cable after seven drives at . 748 naut. west of
final splice. While raising cable, a similar strain as that on the Corinth
end was encountered and it was thought the cable would part; fortunately
this did not occur.
"... endeavoured to recover as much as possible of the
fouled eastern end, but the end could not be brought more than a few
fathoms inboard, so cable had to be cut and abandoned. "
The following quotation indicates how badly crushed the
cable was:
"Recovered . 455 naut. to fresh break, the last . 066 naut. of
which was very badly damaged and flattened, the core having been forced
out between the sheathing wires. By this it was concluded that either a
heavy mass of hard clay had accumulated as the result of the deposit from
mountain torrents and settled down upon the cable, or that there had been
a submarine displacement and the displaced mass had lodged upon the
cable. ’’
The next fault occurred 5 December 1914. Evidently the
cable had been buried by a mass of alluvium carried down by a turbidity
current. A very heavy strain was observed while picking up the cable.
During burial the cable was damaged, since the repair ship's log lists the
fault as caused by a "jag caused by a submarine landslide. "
On 30 October 1918, #1 cable was again broken. The cause
of the break is similar to that for the 1914 repair. A quotation from the
repair ship's log indicates the similarity, and also their awareness of the
cause:
"While picking up, cable was so deeply buried that at times
our gear was unable to clear it. Recovered cable badly damaged and
jagged owing to heavy body falling on cable. In paying out cable it was taken
into deeper water to get it as far as possible from the influence of the
torrents as was reasonable in this instance where the gap was small. "
On 20 October 1919, #3 cable broke in this area for the
first time. It was a typical turbidity current burial and break. The cable
was fouled and could not be cleared by the ship. This is the first instance
95
in this area of rupture due to turbidity current in #3. It is assumed that
#3 lay near enough the land to escape the destructive force of a turbidity
current as it swept down the slope, although it must have been subjected
to considerable chafe. Since #1 cable was not broken at this time, the
current must have been relatively weak. Another contributing factor could
be the fact that #3 cable was 18 years old and probably fairly weak due to
chafe and corrosion by this time.
On December 14, 1920, #2 cable was renewed because a
fault had developed. This cable lies in the basin and well away from
destructive turbidity currents and slumps. However, #2 might be buried
by fine material carried dowr by turbidity currents and deposited in the
basin. The repair log makes no mention of the cable being deeply buried.
However, in 1914 #2 cable developed a fault five miles west of the
1920 fault. During this recovery the log is more specific and we discover
it was indeed buried. Two quotations from the log show how deeply it was
buried:
"... very heavy strain observed while picking up. ”
"... hooked and parted 18 times. M
On 9 December 1921 both #1 and #3 cables broke. (See
Table IV for full report.) Unfortunately the log does not record the
exact times of the breaks. They are typical turbidity current breaks as
is evidenced from the following ship log quotations:
’’The break was caused by the usual submarine landslide,
originated by the heavy torrents from mountain water courses. M
"Cable in poor and damaged state, owing to debris from torrent. Most of
picked up cable had been deeply silted in the mud, and jagged and ruffled,
and in some parts had been (apparently) suspended, as there were trees
and masses of branches and weed entangled about it. "
"We consider, however, that when cable is available and
repairs are necessitated in' this vicinity that extensive diversions of #1
and #3 sections should be effected and thus eliminate the frequent inter¬
ruptions which are invariably caused by the torrents. "
Note that these two breaks fall in line perfectly with the
NNW-SSE trend of breaks. The break in #3 cable is in an area cut by
canyons as shown in Fig. 16, profile 12S. Refer to Table IV (a routine
repair report) and Figs. 33 and 34.
On 9 December 1939, #3 cable was renewed in two places
because of faults. The faults occurred during a heavy gale which also
caused a break in the Bay of Corinth.
96
In 1921 the detour of cable #1 was successful in placing the
cable beyond the reach of the turbidity currents from the Sithas. The
1921 repair of #3 cable moved it further inshore. While this repair moved
the cable off the slope, it left the cable subject to chafe and corrosion on
the shelf.
CONCLUSIONS
The Gulf of Corinth serves as a good example to illustrate
some of the salient oceanographic principles which should be observed in
cable route layout.
First, let us examine the cable failures for the Gulf of Corinth
proper, ignoring The Narrows and Area #2. In this entire area cable #2
never failed due to a tension break, whereas #1 and #3 broke 32 times.
There is a very definite reason for this. Cable #2 was laid directly down
the slope, along the middle of the basin, and directly up the slope on the
eastern end. Cables #1 and #3 run parallel along the continental slope.
These two cables are therefore subjected to sudden strains by turbidity
currents and slumps sweeping down the slope. This type of trouble is
especially common near river mouths, as can be seen from Fig. 32. In
Figs. 39 and 40 it is apparent that cable detours around the river mouths
have been moderately successful in preventing further breaks due to
turbidity currents. There were 20 cases of faults due to chafe, corrosion,
and teredo attack on cables #1 and #3, whereas only eight faults occurred
in cable #2. The cables running along the continental slope parallel to the
shelf edge are subject to chafe and abrasion by slumps and turbidity
currents originating off the many rivers debouching in the gulf.
The breaks in the Alaska communication system cables which
occurred off the mouth of the Katzehin and Stikine Rivers are remarkably
similar to those in the Gulf of Corinth in relative location and cause.
Terzaghi (1957) described similar cable failures in Norwegian fjords which
he attributed to spontaneous liquefaction of the bottom sediments without
horizontal transport. He suggested that the cables sank through the
sediment and broke of their own weight when the bearing strength of the
sediment was diminished by spontaneous liquefaction. However, the
evidence he presented seems to be much more satisfactorily explained in
terms of turbidity currents.
97
It is evident that when possible, cables should be run perpen¬
dicular to the strike of the continental slope. Any cable crossing a
continental slope will be subject in some degree to the same hazards as
the cables traversing the continental slope in the Gulf of Corinth.
98
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