Impacts of the 26 December 2004 tsunami in Eastern Africa

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Ocean & Coastal Management 49 (2006) 873–888

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Impacts of the 26 December 2004 tsunami inEastern Africa

David Obura�

CORDIO East Africa, P.O. BOX 10135, Mombasa 80101, Kenya

Abstract

The tsunami of 26 December 2004 was the largest ever recorded in the Indian Ocean, triggered by the

3rd largest earthquake in 100 years measuring 9.2 moment magnitude. The epicenter of the earthquake

was off Banda Aceh on the Indian Ocean coast of the island of Sumatra in Indonesia, centered at

3.3161N, 95.8541E. A sudden upward movement of the seafloor that averaged �6m occurred along

almost 1300km of the north-east Indian Ocean plate at 0059 Coordinated Universal Time (UTC) and

lasted 8min. Because of the lack of preparedness and absence of warning systems in the Indian Ocean the

tsunami spread silently across the ocean over a span of 8h causing massive destruction including the

deaths of over 250,000 people, with maximum damages occurring in Indonesia, Thailand, Sri Lanka,

India and the Maldives. Moderate to low damages were recorded in the Seychelles, Socotra (Yemen) and

Somalia, though in the latter a highly vulnerable town was impacted resulting in over 300 deaths. Most of

eastern Africa was spared massive damages from the waves due to (a) distance from the epicenter

(46000km), (b) the dissipation of energy of the tsunami by shallow banks in the middle of the Indian

Ocean (the Seychelles banks, Saya de Malha and Cargados Carajos Shoals) and (c) at least for Kenya

and Tanzania, the first and largest waves hit at low tide. In Kenya and Tanzania these factors resulted in

the waves being experienced as tidal surges of 1–1.5m amplitude lasting 5–10min. Damages recorded for

eastern Africa include 11 deaths in Tanzania and 1 in Kenya, of people walking and swimming over

shallow intertidal flats being trapped by the advancing and receding tidal surges, damage to boats

anchored in shallow water and inundation in Mauritius and Rodrigues. Official information, warning

and response networks were nonexistent, and even when an official response was generated in Kenya the

public demonstrated no faith or willingness to act on warnings from officials such as the police.

Importantly, information on the tsunami and the generation of an official response was dependent on

two technologies, satellite television and mobile telephony, and these should be built into future warning

systems as key mechanisms and backups to official information and warning networks.

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ARTICLE IN PRESSD. Obura / Ocean & Coastal Management 49 (2006) 873–888874

1. Introduction

The Indian Ocean covers some 67 million km2 and is ringed by over 22 countries with acombined human population of over 1.5 billion. It is the least well studied of the world’sthree largest oceans, and being ringed almost exclusively by developing countries of Africaand Asia has the lowest levels of resourcing for maritime and environmental monitoringand management. The consequences of this lack of capacity came into staggering focus on26 December 2004 when the largest tsunami ever recorded in the Indian Ocean wastriggered by the 3rd largest earthquake in 100 years (Table 1). Because of the lack ofpreparedness and absence of warning systems the tsunami spread silently across the oceanover a span of 8 h causing massive destruction in its wake including the deaths of over250,000 people [1].A great deal has been written on the origins and nature of tsunamis in general, and the

recent Indian Ocean tsunami in particular [see 2,3]. To date one of the best-recordedtsunamis was that caused by the volcanic collapse of the island of Krakatoa in the SundaStrait, Indonesia in 1883, which caused a tsunami of 37m height that devastated nearbycoastlines on Sumatra and Java and killed 36,417 people [4]. A tsunami is a series of largewaves of extremely long wavelength (several 10 s of km) that travel over 800 kmh�1 usuallygenerated by a violent undersea disturbance such as an earthquake. In this case theearthquake near Banda Aceh on the Indian Ocean coast of the island of Sumatra inIndonesia (Fig. 1) was the 3rd largest earthquake in a century measuring 9.2 momentmagnitude (Table 1). A sudden upward seafloor movement of an average of 6m thatstarted at 3.3161N, 95.8541E and traveled north along 1300 km of the north-east Indian

Table 1

Top ten giant earthquakes of the last 100 years and tsunamis generated by them

Year Source Earthquake Tsunami

22 May 1960 Chile Magnitude 9.5. In Chile 5000 killed, 2

million homeless

Was felt in Hawaii and

Japan

28 March 1964 Alaska Magnitude 9.2. Felt over large area of

Alaska, Yukon and British Columbia

(Canada)

With earthquake, 125

killed, $311 million

damages

26 December 2004 Indonesia Magnitude 9.2 This report

9 March 1957 Alaska Magnitude 9.1. Volcanic eruption and

earthquake

15m tsunami reached

Hawaii

4 November 1952 Russia Magnitude 9.0 Tsunami reached Hawaii,

no lives lost

31 January 1906 Ecuador Magnitude 8.8. Along coast of

Ecuador/Colombia

Tsunami killed up to

1000, felt in California

and Japan

4 February 1965 Alaska Magnitude 8.7 Tsunami about 10.7m

high

15 August 1950 Tibet/India Magnitude 8.6. Destroyed 2000

buildings, worst impacts in northeast

India, 1500 killed

3 February 1923 Russia Magnitude 8.5, in Kamchatka

1 February 1938 Indonesia Magnitude 8.5, in Banda Sea Tsunami damaged islands

in eastern Indonesia

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Fig. 1. The Indian Ocean showing countries of the East African mainland coast and islands of the Central Indian

Ocean. The region covers two time zones—+03:00 Coordinated Universal Time (UTC) on the East African coast,

the Comoros and Madagascar (East Africa Time—EAT) and +04:00 for the islands of the Seychelles, Mauritius

and Reunion (Indian Ocean Time—IOT). Gray curved lines show approximate hourly progress of the tsunami

and the potential influence of the shallow banks of the Seychelles, Saya de Malha (Say.Mal.) and Cargados

Carajos (Car.Car.) in breaking up and reducing the force of the waves. Other abbreviations: Reu/Maur/Rod—

Reunion, Mauritius and Rodrigues. Com—Comoros; Mad—Madagascar; Moz—Mozambique; Tz—Tanzania.

Adapted from UNEP 2005 and an animation on the ITIC website (http://www.tsunamiwave.info/).

D. Obura / Ocean & Coastal Management 49 (2006) 873–888 875

Ocean plate occurred where the India plate subducts beneath the Burma plate. The earthmovement was recorded at 0059 Coordinated Universal Time (UTC) or 0759 local time(0459 IOT; 0359EAT; see caption to Fig. 1 for time zone abbreviations).

The human and socio-economic costs (Table 2) and suffering of southeast and southAsian countries impacted by the tsunami of 26 December 2004 (hereafter refered to as ‘thetsunami’) were as high or higher than the worst natural or manmade disasters, and perhapsbecause of its wide geographic reach, the worst known in recent history. Countries ofeastern Africa were saved by distance from the source from impacts of the samemagnitude, though the eastern tip of Somalia, Socotra Island and the Seychelles did suffersignificant impacts to their populations, infrastructure and natural ecosystems [1].

For the purposes of this paper, the eastern African region is defined as coincident withthe United Nations Environment Programme (UNEP) Regional Seas divisions, namely theislands of the central Indian Ocean (Seychelles, Mauritius, Reunion, Madagascar,Comoros) and the East African mainland coast (Somalia, Kenya, Tanzania, Mozambi-que), and including Socotra Island (part of Yemen, but off the western tip of the Somaliaon the ‘horn of Africa’).

This paper summarizes observations from parts of eastern Africa that were not heavilyimpacted by the tsunami, and focuses on Kenya where observations in response to aquestionnaire were recorded within a month after the tsunami by people along the coast.The reason for this is to document the experience of those parts of the Indian Ocean thatsuffered no or minimal damages from the tsunami, as information on impacts in more

http://www.tsunamiwave.info/

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Table 2

Summary of damage to countries worst hit by the tsunami of 26 December 2004, contained in the UNEP Tsunami

assessment report (UNEP 2005)

Country Region Human Marine environment Land/infrastructure

Indonesia Aceh, northwestern

Sumatra

164,891 buried Seagrass beds (20% loss),

coral reefs (30%),

mangroves ($24.5 million

damage), rivers/wetlands

damaged

Seaside and low-lying

infrastructure destroyed

(roads, towns,

aquaculture/farming,

etc.). Groundwater

salinized. Damage total

$4.45 billion

114,897 missing

412,438 displaced

Thailand Andaman

coast–Phangnga, Phuket,

Krabi, Trang, Satun,

Ranong provinces

5393 dead Seagrass beds (5%

impacted), coral reefs

(13%), mangroves (0.2%)

Seaside and low-lying

infrastructure destroyed

in Phuket (roads, hotels,

buildings), fishing fleets,

1505 ha agricultural land

salinized. No $ estimate

3062 missing

8457 injured

Sri Lanka West and south coast

most strongly impacted

30,000–37,000 dead Coral reefs damaged by

waves/backwash,

mangroves damaged,

seagrass beds intact

4150,000 houses

destroyed, 2/3 of fishing

boats destroyed, coastal

damage was high where

coral mining occurred,

extensive solid waste

transport, groundwater

salinized, coastal roads/

railway destroyed. No $

estimate

Maldives All islands 13,000 displaced Coral reefs intact,

mangroves intact

69 out of 199 inhabitated

islands damaged,

groundwater salinized,

coastal/beach erosion

high, fisheries

infractructure damage.

Damage approx. $400

million

Seychelles Northwest and central

islands (La Digue,

Praslin, Mahe)

No mortality or injuries Carbonate-substrate reefs

highly impacted, granitic

reefs intact. Mangroves

slightly eroded, some

seagrasses smothered

Infrastructure damage at

low-lying points, some

groundwater salinization

and solid waste

movement. Damage total

$30 million

Yemen Socotra island, Al Mahra

Governorate

No mortality or injuries

reported

Underwater assessments

not undertaken

Localized beach erosion

and some groundwater/

well salinization. Major

damage to fisheries

infrastructure, approx.

$1.1-2 million

Somalia Hafun (Horn of Africa) 300 dead, 4500 displaced No assessment possible Waste and hazardous

waste impacts

Numbers were up to date to approximately 5–10 February 2005.

D. Obura / Ocean & Coastal Management 49 (2006) 873–888876

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affected areas were rapidly published following rapid assessments in January–February2005 by UNEP [1] and many publications will appear on highly impacted sites in thecoming years. In the light of initiatives to develop a tsunami warning system for the IndianOcean in UNEP [1], the paper finishes with aspects of the response and reaction to thetsunami in Kenya.

2. Methods

Summary data on the impact of the 26 December 2004 tsunami were obtained at threelevels corresponding to the whole Indian Ocean, eastern Africa and Kenya. For the first,results are summarized from the UNEP Tsunami assessment report [1] which formed thefirst comprehensive analysis of tsunami impacts across the region. Additional informationwas obtained from secondary sources including media, publications and the World WideWeb. For eastern Africa, information was gleaned from media and secondary sources,some personal communications and an email request sent to key respondents known to theauthor. For Kenya, information was collected from the national media (Daily Nation, TheStandard and The East African newspapers), personal communications during the tsunamiand over subsequent days from people known to the author, and from responses to aquestionnaire (Table 3) sent out by email which was then forwarded to others and was alsoplaced in the Coastweek weekly newspaper on January 2005 and in the Malindi MuseumSociety Newsletter for January 2005. Because of the variety of data sources and responses,quantitative analysis is limited, but the sources provide sufficient information for a

Table 3

Survey questionnaire sent by email on 9 January 2004 to 37 recipients

(1) What did you see?

� Where were you on the coast—precisely—town/area, plot y, etc?

� What time did the events start and stop?

� What did you see in terms of the tidal level changing—how high/low, in what amount of time?

� What were the wave conditions—how big were the biggest waves?

� Did the water ever go higher than high tide level, or lower than low tide level?

� When were the conditions worst (at the beginning, end, middle, approximate time y)?

(2) What did you hear about the event?

� Had you heard about the earthquake in Indonesia ?

� Had you heard about the tsunami anywhere?

� How did you hear?

3) did you hear any advice on what to do?

� What was it?

� Who gave it and how (e.g. telphone, text message, ranger on the beach, etc)?

� Did you hear of any official warning?

� Did you see/hear of any official response (e.g. by police, rangers, others)?

(4) Was there any physical damage in your location (e.g. to beach, coastline, shoreline walls, boats, other?)

(5) Any other comments

Some recipients passed it on to others, and it was placed it in the Coastweek weekly magazine and in the

Newsletter of the Malindi Museum Society.


description of tsunami impacts in the low-impact countries of eastern African and inparticular Kenya.

3. Results

3.1. The tsunami

The first set of tsunami waves propagated across the Indian Ocean from east to west(Fig. 1), reaching the Seychelles, Socotra (Yemen) and the tip of Somalia almostsimultaneously approximately 6 h after initiation (0659 UTC, 0959 EAT, 1059 IOT).Points farther south along the African coast, such as Lamu, Kenya and Zanzibar,Tanzania were affected after approximately 8 h (0859 UTC, 1159 EAT). Wave heightsrecorded by tide gauges and available from the University of Hawaii Sea Level Center(UHSLC, Fig. 2) show the decline in wave height from east to west, with wave heightssignificantly exceeding normal tidal variation in Sri Lanka and the Maldives by a ratio of1.6–3.1. A large wave series reached Mauritius, exceeding normal tidal range by a ratio of2.1. The wave height was only slightly greater than tidal variation in the Seychelles andYemen (ratio of 1.2) and less than tidal variation in Kenya and Tanzania (ratio of 0.6).Farther south in Reunion, Madagascar, Mozambique and the Comoros, only minorwaves/tidal surges were reported, likely due to the sheltering effect of shallow banks in themiddle of the Indian Ocean (Seychelles bank, Saya de Malha and Cargados Carajos,Fig. 1).

Fig. 2. Tide gauge data for sites in the Indian Ocean, plotted against Coordinated Universal Time (UTC) for 26

and 27 December 2004. Data obtained from University of Hawaii Sea Level Center (UHSLC, http://

ilikai.soest.hawaii.edu/uhslc/iotd/). y axes are scaled to approximately equivalent full tidal cycles for 25 December

2004, with high and low tide levels shown by the horizontal dotted lines. Numbers on each graph show: on left of

slash, the ratio of maximum/minimum tide levels measured during the tsunami to those measured on 25

December/on right of slash, tidal range in cm measured on 25 December. The three columns of graphs represent:

at right, reference sites where destructive impacts were very high (Mahe, Maldives and Colombo, Sri Lanka);

center, sites where tsunami waves exceeded normal tidal range (Yemen; Mahe, Seychelles and Mauritius); and the

left, sites where tsunami waves did not exceed the normal tidal range (Lamu, Kenya and Zanzibar, Tanzania).

http://ilikai.soest.hawaii.edu/uhslc/iotd/

http://ilikai.soest.hawaii.edu/uhslc/iotd/

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Sum

atra

Phu

ket

SriL

ankaIndi

aM

aldi

ves

Sey

chel

les

Som

alia

Ken

yaT

anza

nia

0

5

10

15

20

25

30

Wav

e he

ight

(m

)

0 2000 4000 6000 8000

Distance (km)

UNEP-min

UNEP-max, r2 = 0.580

Media reports, r2 = 0.867

Fig. 3. Maximum tsunami wave height plotted against distance traveled across the Indian Ocean. Wave heights

are as reported in UNEP 2005 (with minimum also shown where reported), and in the media. The height of the

wave decreased exponentially with distance from the source (r2 ¼ 0:867 for media reports; r2 ¼ 0:580 for UNEP

maxima).


From observations reported in the media and UNEP [1] the primary wave had a heightof up to 30m along the northwest coast of Sumatra (Aceh Province) closest to theepicenter, up to 10m high when it reached Phuket, Thailand, 5–6m in Sri Lanka and thesouth coast of India, 4m in the Maldives, 2.5–3m in the Seychelles and northern Somalia,and about 1.0m in Kenya and Tanzania, approximating an exponential decline in heightwith distance (Fig. 3).

Over 65 aftershocks, some of which measured over 6.0 on the Richter scale, weremeasured following the main earthquake, creating mini-tsunamis in the vicinity of the epi-center [3]. The Seychelles recorded a second set of tsunami waves about 5 h after the first,and two smaller ones 4–8 h later [1]. Observations of the tsunami waves on the Kenya coastextended from about 12:30 to 18:30 EAT, but reporting of later waves due to aftershocks isless certain as these would have occurred at night and at low tide, and were likely onlyvisible on outer reef faces. A second tsunami alert occurred on 5 March 2005 in response toa 6.5 Richter earthquake from the same tectonic source as on 26 December 2004, howeverno tsunami waves were generated. Nevertheless, national alerts were sounded in a numberof countries, including the Seychelles, Mauritius and Kenya.

3.2. Somalia, Socotra, Seychelles

Significant impacts from the tsunami were reported from northern Somalia, Socotra andthe Seychelles (Table 2 and [1]). Because these areas were inundated by waves above thehigh tide line, damage to coastal infrastructure and terrestrial features was significant, aswas the potential loss of life. Impacts in these countries were patchy, focused on low-lyingland adjacent to the sea. In the Seychelles and Socotra these are restricted to narrow bays


or river mouths, around which damage was focused. By contrast, the coast of Somalia isdominated by broad sandy plains just above sea level [5], with extensive settlement on theupper-beach and dunes such as at Hafun. Hence the massive impacts in terms of loss oflife, and movement and damage to hazardous waste stores [1]. It is notable that the tidegauge data for Yemen (Fig. 2) shows an extended period during the night of 26–27December when the mean tidal level was near the high tide mark and tsunami surgesexceeded normal high tide levels, unlike other sites where the tidal pattern followed a moreregular sine-curve with only brief periods at maximum high tide.The major classes of impact in these countries are summarized from the UNEP Tsunami

assessment report [1] and include the following:

�
Physical damage to shoreline and infrastructure. Shorelines less than 1–2m above sealevel were vulnerable to inundation by the tsunami depending on offshore topography.Construction and development tend to focus on flat coastal plains and these were mostvulnerable, particularly evident at Hafun in Somalia and areas such as Mare Anglaiseand the Port on Mahe in the Seychelles. � Loss of human life, generally from the surge of waves onshore and subsequent
backwash into the sea. This occurred at Hafun in Somalia where the town wasinundated by the waves. In the Seychelles and Socotra, most human habitation is higherabove sea level on sloping rocky shores, and there was fortunately no mortality from theinundated areas mentioned above.
� Backwash of materials and waste into the sea. Physical debris broken and displaced by
the waves was evident at all locations surveyed, both on beaches, in the shallows andsubtidally in coral reefs and seagrass areas in the Seychelles [6].
� Damage to subtidal and intertidal habitats. Underwater surveys were only conducted in
the Seychelles. Here significant damage occurred to coral reef frameworks weakened bynear total mortality of branching corals in 1998 that had only partially re-cemented bythe time of the tsunami. Such reefs suffered a second near-total destruction by waveaction of the tsunami.

3.3. Mauritius, Madagascar, Comoros, Mozambique, Reunion

Apart from Mauritius, observations of the tsunami from these countries were minimal.A minor tidal surge was reported from Mayotte, part of the Comoros group of islands(F. Seguin, pers. commun.), but with no impacts noted on land or in the sea. The othercountries and islands in this group were likely sheltered from the tsunami waves by shallowbanks in the middle of the Indian Ocean, i.e. the Seychelles banks and Cargados Carajosshoals, reducing the energy stored in the waves by the time they crossed the ocean.Observations from Mauritius have been obtained from the island of Rodrigues

(E. Hardmann, pers. commun.). Rodrigues was hit by 7 waves occurring between about1000 and 1700 IOT, with the water level reportedly rising approximately 2m above thehighest high tide level. Coastal areas including the main town, Port Mathurin, wereflooded. An artificial sand island (Ile Hollandaise, created from dredged material from theshipping channel) suffered erosion and was split into two, and erosion has also beenobserved on sandy beaches in the south–east of the island. Smothering of corals at 6–12m


depth, by sediment moved by the tsunami, was reported in the vicinity of Port Mathurin,however, no physical damage or overturning of corals was recorded at any sites. For 2months following the tsunami, observers commented that high and low tides were moreextreme than usual. It is uncertain whether this might have been due to relative changes inshoreline, movement of sandbars, or oceanographic phenomena, or the result of subjectiveobservation errors.

Other than the above observations, minimal damage was reported from Mauritius,perhaps because the normal tidal range on 25 December 2004 was only 56 cm (Fig. 2), andthough two to four times larger than this, the tsunami was sufficiently dissipated to causeminimal damage.

3.4. Tanzania

Unusual tidal conditions reported for Kenya (below) were also experienced in northernTanzania [7]. However neither physical damage to the shoreline nor underwater impacts tocoral reefs have been reported from Tanzania. Tragically, 11 deaths occurred in the vicinityof Dar es Salaam, due to the extremely strong currents caused by tidal surges overintertidal flats. Newspapers reported them to be young, and possibly a family group [8].

3.5. Kenya

Primary observations for this section are summarized from observations reported inKenya, collected through a questionnaire sent out by email and in the local press from 26respondents to a questionnaire circulated in January 2005 [9]. Impacts were likely to besimilar at adjacent locations in southern Somalia, and along the whole mainland coasts ofTanzania and Mozambique, diminishing from north to south (Fig. 1). Unlike sites closerto the origin of the tsunami, in Asia and even the Seychelles, Kenya experienced tidalsurges, not breaking waves. Fortunately the tsunami height of approximately 1m, and theeffects of traveling 6000 km across the ocean prevented the buildup of a breaking wave onencountering shallow water.

Of the 26 questionnaire respondents, 16 were female and 10 male, and spread betweenthe following status: coast residents (13), reef/marine-oriented business owners (7), Kenyanresidents on holiday on the coast (3), government official (1), newspaper reporter (1),foreigner (1). Observations were received from the whole Kenya coast (Fig. 4), fromMkokoni/Kiwayu island in the north to Pemba channel in the south and with greaternumbers of respondents in the central regions.

The earliest observations in Kenya were from 1230 EAT during a spring tide cycle as thetide was rising from a low of 0.5m at 1024 EAT to a high tide of 2.6m at 1631 EAT(Fig. 5). Full spring tides range from �0.1 to 4.1m, thus maximum and minimum tides onthe 26 December were well within normal ranges. Observations were made until about1830 EAT, though several respondents indicate tidal surges did occur at night, but werelargely unobserved due to the broad expanse of reef exposed on the spring low tide.

At 1230 EAT, the tide was rising and reportedly first dropped by about 1m, exposingintertidal flats that had just been covered by the rising tide. The clearest descriptions of thetsunami wave itself were from Malindi, where observers noted a wave approaching ‘fromthe north’ at a 451 angle to the coast (see Fig. 1), visible as a bulge in the sea beyond thereef. Because the coastline in Malindi lies in a northeast–southwest direction, a 451 angle

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Fig. 4. Map of the Kenya coast showing the distribution and number of questionnaire respondents.

D. Obura / Ocean & Coastal Management 49 (2006) 873–888882

actually implies a more easterly direction to the wave, corresponding to the mainwavefronts depicted in Fig. 1. Malindi bay opens towards the north with a relativelyexposed beach, and as the wave swept in reef waters became choppy, appearing to be‘boiling’. The wave front was breaking and foaming over the reef and shallows and ontothe relatively exposed beaches, causing immediate beach erosion and damage to anchoredboats. At other locations in Kenya, the tsunami was less clearly wave-like and descriptionsemphasize strong surge currents through channels or over shallow reef flats and beaches.Thus, the effect was more akin to tidal surges or rapid cycles, with a full in-out cycle lasting10min with an amplitude of 1–1.5m.Observations vary, but the largest number of down-and-up surges reported was 8–10,

with the last one occurring around 1800 EAT, just after high tide. Surges were apparentlynot evenly spaced, occurring in clusters with gaps of stable tide levels in between. Ingeneral observers indicated that the first surge was the largest and strongest, between about1230 and 1330 EAT, with decreasing amplitudes later during the day. Reports of theminimum and maximum water levels with respect to normal low and high tide varied,though these are only indicate as respondent’s views on this is very subjective. Theobservation from Mkokoni/Kiwaiyu in the north noted that the tidal surge reached both

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-200

-150

-100

-50

0

50

100

150

200T

ide

heig

ht, c

m

0 6 12 18 24 6 12 18 24

Dec 26 Dec 27

Fig. 5. Tide levels from 26 to 27 December 2004 as documented by tide gauges (heavy line, see Fig. 2 for source)

and high/lows predicted by Tide Charts for Lamu (Grey circles, Kenya Tide Tables 2004) plotted on East Africa

Standard Time (EAT). Vertical red lines show estimated maximum tidal surge amplitude based on questionnaire

responses (1–1.5m, centered on the tide height) starting at 12:30 h and ending at 18:00 h. Potential tidal surges

during the night are also shown (dashed red lines). The figure clearly shows that tsunami effects fell well within the

envelope of tidal variation for the Kenya coast, not exceeding maximum spring high tide levels of 4–4.1m

(+200 cm on the y axis) and not falling below minimum spring low tide levels of 0m (�200 cm).


extreme low and high tide levels. Only one other observer, from Malindi, stated that thetidal surges reached normal neap low and spring high tide levels. For all sites at least fromLamu southwards, it seems likely that the tidal surges never dropped below maximumspring low tides, nor rose above maximum spring highs.

During the surges, strong currents were observed, causing rippled and choppy surfacewaves up to knee high, with one estimate of 4–5 knot currents. Many observers noted thatwaters were brown and turbid, from stirring of sediments during the surges. Choppysurface waves were noted from Malindi, Bamburi and Pemba channel. Where theyoccurred, choppy rough conditions were likely due to conflicting currents due to the tidesand tsunami surges, not to the tsunami wave itself breaking. Particularly in Malindi Baywhich is not protected by a fringing reef unbroken ocean waves interacted with tidalcurrents, all magnified by the orientation of the bay facing north trapping the wavefrontsand forcing them to break in the bay. Other areas were apparently calm such as in Nyali,with different observers observing ‘glassy’ or ‘choppy’ conditions. At Mkokoni/Kiwaiyu inthe north and Pemba channel in the south fishing boats offshore did not notice the tsunamiwaves at all.

Sand movement and reorganization of beach profiles was reported for northern Kenyawhere soft substrate habitats predominate and the waves were largest. In Lamu, thetsunami caused a dramatic reorganization of beach structure, eroding 1–2m of sand froma channel-edge beach at Shela village and constructing new sandbars in the open bay infront of the island. Because the waves did not exceed the high tide line, no damageto shore-based infrastructure was noted, including in Kilindini Harbor in Mombasa,where the Kenya Port Authority was on alert having noted the rapid changes in waterlevel.

Subtidal impacts of the tsunami waves in Kenya were limited. Only one clear case of alarge coral head being overturned by the waves was noted, in the Kiunga Marine National


Reserve. This was of 43m diameter plates of Turbinaria mesenterina in a high-currentmangrove creek channel that had been in place for the preceding 7 years and untouched byregular tidal currents (pers. obs.). Other cases of slumped large coral boulders andbommies may have been from regular storm waves and tidal currents. Over 300 markedcoral colonies on shallow lagoon reefs (o0.5m) in the Mombasa area showed no signs ofdamage or overturning from the waves (S. Mangubhai, pers. commun.).The primary damage reported was to boats and fishing gear. Many boats at anchor were

dragged due to pulling of their anchors, knocking against each other and sufferingdamage. Malindi reported the highest level of damage to boats due to the exposedorientation of the bay and many boats were deposited on the beach. Fishing gear (e.g. nets,traps, lines) on boats and on the beach in Malindi were also lost. There were few confirmedreports of similar damage in other parts of Kenya, where boats were either saved or boatowners where on-hand managing their boats as the surges came in and out.The 26 December is a public holiday in Kenya (Boxing Day), thus many public and

recreational beach areas are very crowded with people from late morning onwards. Manypeople entering the water on the beaches, taking advantage of the shallow waters on therising tide, reported strong currents especially during the receding phase of the waves.Reports from Mombasa indicate currents were strong enough to pull people out. The onefatality reported for Kenya was of an upcountry man visiting the sea for the first time andentering it to learn how to swim [10]. By the time others around him noticed that he hadbeen dragged away, it was too late to save him.Ironically, news of the tsunami was available in East Africa by about 1000 EAT, 2–3 h

before impacts locally, from global cable television networks such as CNN, Fox News andthe BBC World Service. Even more pertinently, a yacht router based in France gaveaccurate warnings to clients that contacted the company for information, accuratelypredicting the scale and timing of waves reaching the east African coast.

4. Discussion

The eastern African region was significantly impacted by the tsunami, particularly forthe easternmost islands and landmasses including the Seychelles, Socotra and at Hafun onthe horn of Somalia. At these locations the height and volume of the tsunami waves weregreater than normal tidal ranges, and were experienced as breaking waves. They weresufficient to cause significant physical damage on low-lying coastal areas includingflooding and damage to physical infrastructure such as seawalls, beachfronts and roads,and in Hafun where there was human habitation immediately above the beach there weresignificant deaths (Table 2, [1]). Where underwater damage assessments were conducted(e.g. in the Seychelles, [6,11]) significant damage was recorded to underwater habitats suchas coral reefs and seagrass beds.The westernmost parts of the region, including most of the east African mainland coast

(southern Somalia, Kenya, Tanzania, Mozambique) and the other islands (Mauritius,Madagascar, Comoros, Mayotte, Reunion and the western islands of the Seychelles),experienced significantly smaller wave heights, in many cases less than normal tidal ranges.Further, the tsunami ‘waves’ were experienced as tidal surges lasting 5–10min, as opposedto breaking wavefronts. At these locations coastal flooding was only reported for theislands of Rodrigues and Mauritius, and deaths were only reported from Kenya (1) andTanzania (11), where people wading on sandflats or in the shallows were overcome by the


intense currents generated by the tidal surges. In Kenya the victim was known to be a non-swimmer, and the majority of victims in Tanzania were in one family party, also likely tobe non- or poor-swimmers.

Three factors are likely to be the most important in minimizing impacts of the tsunami inthe eastern African region:

(a)
Most of the region lies at least 6000 km from Sumatra and the earthquake epicenter(Figs. 2–4) resulting in diminution of the wave energy and therefore height. Even at4500–5000 km the Seychelles and tip of Somalia experienced large and damagingwaves. The epicenter of the volcanic explosion that destroyed Krakatau and senttsunami waves across the Indian Ocean in 1883 is in the same geographic region,further south and east along the Sumatra–Java chain of islands in Indonesia.
(b)
The Seychelles banks, bearing the central granitic islands and several outer corallineislands of the Seychelles, and other shallow banks such as the Chagos Archipelago,Saya de Malha and Cargados Carajos shoals lie in the middle of the Indian Ocean(Fig. 1). These banks vary between 10 and 30m depth, which would cause significantdissipation of tsunami waves with wavelengths on a scale of 10–100 km. The shallowwaters of the Seychelles bank were implicated in the much-reduced impact of thetsunami on more centrally located islands on the plateau compared to those on theeastern edge ([1,6]), and this effect likely sheltered all areas located in a broad swathfrom southern Kenya to Reunion and including Tanzania, Mozambique, Madagascar,Comoros, Mayotte and the western islands of the Seychelles (Fig. 1).
(c)
The first set and largest tsunami waves were experienced at low tide throughout theregion, and certainly in Kenya and Tanzania, and likely in Somalia, minimizing theirthreat to land above the high tide line.
Because of the first two of these reasons, most of eastern Africa is likely to be relativelysafe from future tsunamis from the same tectonically active region, though the third factor,that the tsunami reached East Africa at low tide, was serendipitous. Nevertheless, a largerearthquake is theoretically possible (see Table 1), and the magnification of a few decimalpoints up the Richter scale could yet be disastrous for the region. There are no closerearthquake sources of a similar magnitude for the Indian Ocean seafloor. Two other areasthat register as earthquake epicenters include the Bengal Plate off India and a volcanicallyactive zone off northeastern Madagascar and the Comores [3]. The latter registered anearthquake of Magnitude 5.0 on 5 January 2005, though the epicenter apparently does nothave the characteristics for generating tsunamis, being too deep in the earth’s crust. As yet,no tsunamis or wave disturbances have been reported from these or other sources in theIndian Ocean.

The lack of a tsunami warning system for the Indian Ocean undoubtedly contributed tothe massive human mortality recorded in all countries at least 1 h distant from theepicenter, and in the case of the eastern African region, all the deaths recorded there.Physical damage was minor in relation to countries closer to the epicenter, though it isclear that tsunami damage prevention measures would have further minimized damages inthe Seychelles, Socotra and Somalia. Accordingly, intergovernmental initiatives toestablish a tsunami warning system for the Indian Ocean comparable to that in thePacific are underway [12,13], and will include identification and funding of a centralcoordinating body with links to earthquake and tsunami warning capabilities within and


outside the region, and embedded in a more general hazard early warning and responsecontext.Private-sector/independent communication channels (cable television and a maritime

information service provider) provided the only available information resource for easternAfrica, and would have been sufficient to raise a coordinated response that couldtheoretically have eliminated all loss of life in East Africa. However one either had to havedirect access to cable television and the knowledge to interpret the information, or one hadto know the contacts for private information sources to access them. However thisinformation served no public purpose without the mechanisms for interpreting andchanneling it to the right decision nodes and subsequent communication to the publicand local authorities. Formal tsunami warning responses for the Pacific, while awareof the earthquake in Sumatra and presumably of the likelihood of an Indian Oceantsunami, were unavailable for call-in queries on tsunami likelihood or responses in theIndian Ocean (pers. obs.), and their only reported unofficial means of communication,through US embassies and contacts in countries of the region [14] were unavailable orineffectual.In Kenya, two sets of mechanisms were set in motion that resulted in some level of

public announcement of the tsunami threat, however both were marred by unclearchannels for decision-making and action, and they occurred only as responses to observedconditions locally not to advance warnings. The first involved observations with theMombasa Port by the Kenya Ports Authority (KPA) of unusual and changing tidalconditions from about 1200 EAT. This resulted in a local radio and police announcementin Mombasa, and checks by KPA officials at other minor ports (e.g. in Lamu) by 1800EAT, but with little generalized response. The second involved channeling of observationsfrom people along the coast through mutual contacts eventually to the Ministerial leveland subsequent radio warnings and police action to clear public beaches. But final actiondid not occur until about 1800 EAT when the worst of the waves had already passed.In both cases (a) an early warning system would have enabled timely responses, and (b)emergency channels of communication and response to police and local authorities werenot well known or practiced. In the second example, none of the communications wouldhave occurred without mobile phone and text messaging technology, and this should bebuilt in as a core platform for any future communication and response plans. Lastly,even where a local response to clear the beaches was attempted the public in general had tobe almost ‘beaten from the beaches,’ not having any sense of trust or belief in thewarnings being given them even by personnel in authority such as marine park rangers orthe police. To be effective, future warning systems will have to include public awarenessdrives.Many countries in east and southern Africa suffer drought and flood warnings on an

almost annual basis as changing regional weather patterns and environmental degradationcombine to increase vulnerability of natural and agriculture ecosystems. Typically,national disaster initiatives and institutions have focused on these drought and flood-related hazards, evidenced by membership and hosting of disaster response committees; inKenya primary responsibilities rest with the Meteorological Department (warning:weather and climate prediction) and the Office of the President (response: security andresource mobilization). Severe drought and famine across much of Kenya in early 2006,and the lack of early preparedness and avoidance strategies nationally, emphasize howeven with the most commonly faced hazards capacity lags far behind current needs.


Similarly, the impacts of and response to the tsunami in East Africa relate strong lessonson the state of coastal disaster preparedness in countries of the region. The strongestregional instrument relating to the environment, the Nairobi Convention (the Conventionon the Protection and Development of the Marine and Coastal Environment of theEastern African Region), to which all states in Eastern Africa are party, addresses issues ofmarine pollution and protected areas, but does not contain language relevant to hazard ornatural disasters or hazard preparedness. Partly as a result of this marine and coastalhazard preparedness have been subordinate to other regional priorities. While the conceptsof Integrated Coastal Zone Management have been rapidly adopted under the umbrella ofthe Nairobi Convention, natural hazard and disaster preparedness have not featured inkey national documents and processes e.g. [15,16]. The most significant hazard to strikecoastal regions in the region prior to the tsunami, the severe flooding in Mozambique in2001, found disaster warning and preparedness in relation to inundation of low-lying areascompletely lacking.

In spite of the lack of concerted coastal hazard preparedness, a number of initiatives doserve as a foundation. For example, the Eastern African Coastal and Marine EnvironmentResources Database and Atlas project of the Nairobi Convention/UNEP Regional Seasprogramme in the late 1990s provided the first recently updated maps of major resourcesand infrastructure in selected countries e.g. [17], though at very course national resolution.These then formed the basis of coastal datasets in National Oceanographic Data Centersin each country. Building on this, a recent Kenya–Danish collaboration project (KenSeaproject, Environmental Sensitivity Map for Coastal Area of Kenya) is building a GISdecision-support tool for oil spill mitigation, providing the first detailed inundation riskmaps for the Kenya coast. Nevertheless such information resources are patchy, are oftenbased on incomplete datasets due to historically low investment in long term datacollection at national levels and may need additional resources to generalize them to otherhazards (in this case such as high waves or storm surges). With respect to minimizing riskfrom hazards, zoning and building restrictions along coastlines in the region are generallynonexistent, or where present poorly conceived and formulated, and regularly flouted,providing a wholly inadequate foundation for minimizing inundation risk and responsecapability.

Appropriately, among the most significant consequences of the tsunami is theenergizing of national, regional and global undertakings to develop tsunami andnatural hazard warning systems that cover the Indian Ocean as part of global warningnetworks [12]. These new-generation warning systems are explicitly being developed tocover multiple marine and coastal hazards and cover the full range of capacitiesincluding data and information systems, communication networks, and intergovern-mental commitments and national response capacities [18]. They must also incorporateadaptive mechanisms and private sector partners to compensate for institutional inertiain government sectors. The mainland coast of East Africa and the western IndianOcean Islands were fortunate in the low impacts experienced from the December 2004tsunami. However population growth, migration to coastal zones, long-term environ-mental degradation and resource overexploitation and Global Climate Change will allcontribute to greater vulnerability of people, infrastructure and ecosystems oncoastlines. Improving disaster preparedness and warning systems to minimize theimpacts of these threats should become one of the most important long-termconsequences of this recent event.


Acknowledgments

Many individuals contributed information incorporated in this manuscript, andimproved the text. I would like to acknowledge Ali Mohammed, Ann Robertson, BrendaBrainch, Bruce Phillips, Carol Korschen, Chris Angell, Flora Mutuga, Hussein Alidina,James Nokes , Joan Nesbitt, Kate Moran, Korinna Cowan, Lisa Pelizzoli, Lulu Archer,Melinda Rees, Mohammed Omar, Nicky Parazzi, Paul Krystall, Paula Kahumbu, Ralphand Lucy Diaper, Ralph Winter, Sangeeta Mangubhai, Sayaka Tsutsumi, Shakil Visram,Simon Englefield, Stephanie Maxwell, Sylvia Delap and Ulrike Neubert.

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Impacts of the 26 December 2004 tsunami in Eastern Africa