The Galapagos Islands: a Laboratory for the Study of ...dgeist/Chapman/ChapmandOzo… · • A look at other oceanic islands - • Comparing islands within the archipelago - Tortuga

The Galapagos Islands: a Laboratory for the Study of Hydrological Processes

Noémi d’Ozouville, Alexandre Pryet, Sophie Violette & the GIIWS team

Collaboration with Charles Darwin Foundation, Galapagos National Park, Consejo de Gobierno & Municipal Government of Santa Cruz

AGU Chapman Conference, Galapagos, July 2011

Already proven as a Laboratory for Evolution!

P. Hoeck

and a Laboratory for Geological Processes!

Godfrey Merlen, 2009Godfrey Merlen, 2009

Tom Simkin, Smithsonian, 1968

Why Hydrology in Galapagos?��

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Controlled Conditions 1-

Geological Setting


Climatic Setting

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NASA/JPL NASA/JPL www.cmi2.yale.edu

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http://www.cmi2.yale.edu

http://www.cmi2.yale.edu


Geomorphological SettingSANTA CRUZ

SAN CRISTOBAL

Hydrological Processes 1-

Where do we start?

• Problem in Galapagos was not the “complexity”

• Simply there was no data ....

and very limited freshwater resources on the surface.“The main evil under which these islands suffer is the scarcity of water. [...] Everywhere the porous nature of the Volcanic rocks has a tendancy to absord, without again throwing up, the little water which falls in the course of the year.” Darwin (1836)

• Few outcrops, few wells, few springs, few roads.

• Historical data - from 1535 to 1950s.

• Anecdotal data - tortoises, fishermen, farmers and researchers.


What can we learn locally?

20082000


Comparative approach• A look at other oceanic islands -

• Comparing islands

within the archipelago -

Tortuga Bay Media Luna

« grieta »fault scarp

S N

0 5 10

0 m

400 m

800 m

200 m

600 m

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Paci!c Ocean

salted water

brackish water

fresh waterbasal

aquifer

potentialperched aquifer

dyke

neck

faultshield seriesformations

platform seriesformations

« pozo profundo »drillhole

Volcanic Formations Discontinuities


« grieta »fault scarp

S N

0 5 10

0 m

400 m

800 m

200 m

600 m

km

Paci!c Ocean

salted water

brackish water

fresh waterbasal

aquifer

potentialperched aquifer

impervious layer(welded ash, red soil)

dyke

neck

fault

shield seriesformations



Volcanic Formations Discontinuities


grieta

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paci!c ocean

salted water

brackish water

fresh water

basalaquifer

perched aquifer

dyke

neck

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shield seriesimpervious hydro-thermalized core

km0 5 10

0 m

400 m

800 m

600 m

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Basal aquifer + dykes Basal + perched aquifer High level basal aquifer

10 0000,1 Ma1 Ma10 Ma100 Ma

Floreana (1.5-0.07 Ma)

Santa Cruz (0.59-0.05 Ma)

South San Cristóbal (2.3-0.6 Ma)

Sierra Negra, Isabela(9000 - ...)

Kauai Oahu

MauaiHawaii

Easter Island

Azores (Terceira, Pico)

Canaries (Teneri!e)

Cabo Verde (Fogo)

Réunion Island

Madère

Galapagos Islands Integrated Water Studies (GIIWS)

?

Quanti!cation of Rechargeinput from precipitations and interceptionof fog water by the vegetation.climatic records, instrumentation of soil and vegetation

TASK 2Morphology and Hydrogeology of volcanic formationsgeophysics, remote sensing, !eld works

TASK 1

Groundwater dynamicsconceptual model, analytical and numerical modeling

TASK 3

Timeline & Highlights

• 2003 - Start of project, first field trip - discovery of rivers on San Cristobal!

• 2004 - Digital Elevation Model! Combined radargrammetric & SRTM data

• 2004-2005 - First hydrological meteorological data

• June 2005 - A new look on the islands! GoogleEarth!

• 2006 - Helicopter-borne Time Domain electromagnetism

• 2007 - PhD defense

• 2008 - New PhD student

• 2010 - ANR 3-year grant, agreement with Escuela Politecnica Nacional

• 2010 -2011 - Watershed scale monitoring Santa Cruz

Where we are now ...

• Surface hydrology:

- Forms

- Hydro-ecological monitoring

• Groundwater:

- Study of the basal aquifer

• Hydrogeomorphological evolution

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Surface Processes 1 - Climate

• Climatic data (Trueman & d’Ozouville, 2010), Huttel, 1995 - variable P and more constant T .

• What is happening now? 2008 and 2011, two of the four rainiest years in 40 year record - 1982/1983 & 1997/1998 = Regional Mega- El Niño events. 2005-2006 during my PhD - 1 rainfall each year! no mas!

• 2008 and 2011 - La Niña conditions in the Pacific, warm water anomaly in Galapagos = rain, preceded by anomalously cold T garua season.

Rainfall (mm)ECCD - 5m Bellavista - 180m

Trueman & d’Ozouville, 2010

Surface Processes 2 - Forms Foto Aéria 16-04-1985

d’Ozouville, 2007

Surface Processes 2 - Forms

March 2010, Flash flood

event

March & April 2011, regular activation of

channels after months of rain.

N. d’Ozouville

N. d’Ozouville

N. d’Ozouville

N. d’Ozouville

Surface Processes 3- Soils

Adelinet et al., 2008

Surface Processes 4- Watershed instrumentation

Surface Processes 5- Water Balance 2005-2006

Rainfall ~ 1251 mmRunoff = 14400 m3

0,13 km2

mm/year % rainfall % eff. rainfall

ETR 735 59

Runoff 113 9 22

Infiltration 403 32 78 d’Ozouville, 2007

Surface Processes 6- Hydro-ecological monitoring

2010-2011 Hydrological year

- Throughfall, interception and evaporation (Gonzalez et al., poster session; Dominguez, et al., 2011, EGU; Pryet et al., submitted)

- Stemflow data (Fuentes et al., 2011, EGU)

- Sapflow data from garúa season (Fuentes et al., 2011, EGU)

- Fog drip condensation data

Linking surface process and subsurface processes

N. d’OzouvilleN. d’Ozouville N. d’Ozouville

N. d’Ozouville

N. d’Ozouville

N. d’Ozouville

Subsurface Processes - Basal & High-elevation Aquifers

• Basal aquifer has been- Seen on Isabela, San Cristobal

- Seen and monitored on Santa Cruz

- Visualized by geophysics on Santa Cruz & San Cristobal

• High-elevation springs are- Type 1: Associated with parasitic cones - Seen & monitored on San Cristobal, Floreana & Santa Cruz

- Type II: Seen & monitored on San Cristobal; & visualized through geophysics on Santa Cruz and San Cristobal.

Basal Aquifer on Santa Cruz

N. d’Ozouville

A. PryetA. Pryet

N. d’Ozouville

Basal Aquifer Monitoring

!

Electrical Conductivity2 - 8 ms/cm @ 25oC (2 to 16% Sea water)

!

Temporal variation

5

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GIIWS Data SetGIIWS, 2011


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A. Pryet, 2011


E. coli concentrations in the basal aquifer: <5 UFC

5-50 UFC

>200 UFC

!Jessie Liu, 2011

Methodology Slide - SkyTEM

method, SkyTEM (Sørensen and Auken, 2004) (Fig. 1b), give sufficientinsight to understand the internal structure of the volcano. Over900 km of profile transient data (covering an area of approximately190 km2) were gathered in 8 days (Fig. 1a).

2. Methods

SkyTEM (Sørensen and Auken, 2004) is a transient electromagneticsystem where weak subsurface currents are induced by a very strongcurrent flowing in the transmitter coil. The subsurface currents diffuseinto the ground with a magnitude and decay which are related to theconductivity of the geological layers (Fitterman and Labson, 2005). Thedata which is measured in the receiver coil (Fig. 1b) is the time de-rivative of the magnetic field from the decaying subsurface currents.

Average helicopter flying speed was 45 km/h during the Santa Cruzsurvey and the flight altitude of the rig was 35-45 m. In general lineswere oriented South–North and the average spacingwere 200m.A fewlines were flown cross island to obtain a full picture of the salt-freshwater interface. Navigation data (flight altitude, tilt of the frame, GPSposition) are processed and the data itself are filtered by trapezoid-shaped filters (Auken et al., 2007) in order to suppress natural back-ground noise. The filters were designed to enhance near-surfaceresistivity variations by avoiding any smoothing of the early time data.At later times data were more severe filtered to obtain as muchdepth penetration as possible. After filtering, data are gathered intosoundingswith a spatial distance of about 25m. The inversionmodel isdescribed by a number of layers, each with a thickness and a resistivity(Auken and Christiansen, 2004). The soundings are inverted using the

Fig. 1. Overview map showing the Santa Cruz Island, the SkyTEM flight lines and SkyTEM system in operation. a) Santa Cruz is a central island in the Galapagos Archipelago (inset).Shown are the limited permanent water resources of the island (H): a unique low-outflow, highland spring (450 m a.s.l.), a single deep brackish water well (elevation: 160 m a.s.l.),and coastal open fractures called “grietas”with brackish contaminated water (elevation: 5-15m a.s.l.). Data acquisition flight lines carried out during the SkyTEM survey are shown inblack over topography (DEM from (d'Ozouville et al., in press)). b) SkyTEM instrumentation hangs in a rig 30m below the helicopter which flies 60-75m above the ground surface at aspeed of 45 km/hour on average.

Fig. 2. Two cross-sections reveal the internal structure of Santa Cruz Island and four units of hydrogeological interest. The positions of the south-north and west-east profiles acrossthe island are shown on the inset over a background of near-surface average resistivity showing extent of mapped area. The profiles show the density of data generated and thepenetration depth of between 200 and 300 m. The four units of hydrogeological interest are: (I) High-resistivity unsaturated basalts; (II) Seawater intrusion wedge underlying thebrackish basal aquifer; (III) Near-surface, low-resistivity units consisting of colluvial deposits; (IV) Internal, low-resistivity unit of saturated basalts overlying an impermeable stratum.

519N. d'Ozouville et al. / Earth and Planetary Science Letters 269 (2008) 518!522

Survey :

SkyTEM helicopter-borne TEM Penetration depth: 0 m – 250 m 350 km of flightlines, 300m - spaced 23000 soundings, 1 sounding every 15m

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Inversion models:

Laterally constrained models - 4-layer / 18 layerdʼOzouville et al., 2008

Quasi 3D spatially constrained inversion (Viezzoli et al., 2008) => 19 layers “smooth” model => 4 layers model

Basal Aquifer Visualization

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Depth to Interface with sea water (SWI) from SCI 19L

- Visible put to 9 km inlandhydraulic gradient 0,005

- Present all around the island

- At deep well : -33 a.m.s.l.

=> Ghyben-Herzberg height of freshwater lens is less than 1 m a.m.s.l.

Pryet et al., 2011

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High-Level Aquifer on Santa Cruz?

method, SkyTEM (Sørensen and Auken, 2004) (Fig. 1b), give sufficientinsight to understand the internal structure of the volcano. Over900 km of profile transient data (covering an area of approximately190 km2) were gathered in 8 days (Fig. 1a).

2. Methods

SkyTEM (Sørensen and Auken, 2004) is a transient electromagneticsystem where weak subsurface currents are induced by a very strongcurrent flowing in the transmitter coil. The subsurface currents diffuseinto the ground with a magnitude and decay which are related to theconductivity of the geological layers (Fitterman and Labson, 2005). Thedata which is measured in the receiver coil (Fig. 1b) is the time de-rivative of the magnetic field from the decaying subsurface currents.

Average helicopter flying speed was 45 km/h during the Santa Cruzsurvey and the flight altitude of the rig was 35-45 m. In general lineswere oriented South–North and the average spacingwere 200m.A fewlines were flown cross island to obtain a full picture of the salt-freshwater interface. Navigation data (flight altitude, tilt of the frame, GPSposition) are processed and the data itself are filtered by trapezoid-shaped filters (Auken et al., 2007) in order to suppress natural back-ground noise. The filters were designed to enhance near-surfaceresistivity variations by avoiding any smoothing of the early time data.At later times data were more severe filtered to obtain as muchdepth penetration as possible. After filtering, data are gathered intosoundingswith a spatial distance of about 25m. The inversionmodel isdescribed by a number of layers, each with a thickness and a resistivity(Auken and Christiansen, 2004). The soundings are inverted using the

Fig. 1. Overview map showing the Santa Cruz Island, the SkyTEM flight lines and SkyTEM system in operation. a) Santa Cruz is a central island in the Galapagos Archipelago (inset).Shown are the limited permanent water resources of the island (H): a unique low-outflow, highland spring (450 m a.s.l.), a single deep brackish water well (elevation: 160 m a.s.l.),and coastal open fractures called “grietas”with brackish contaminated water (elevation: 5-15m a.s.l.). Data acquisition flight lines carried out during the SkyTEM survey are shown inblack over topography (DEM from (d'Ozouville et al., in press)). b) SkyTEM instrumentation hangs in a rig 30m below the helicopter which flies 60-75m above the ground surface at aspeed of 45 km/hour on average.

Fig. 2. Two cross-sections reveal the internal structure of Santa Cruz Island and four units of hydrogeological interest. The positions of the south-north and west-east profiles acrossthe island are shown on the inset over a background of near-surface average resistivity showing extent of mapped area. The profiles show the density of data generated and thepenetration depth of between 200 and 300 m. The four units of hydrogeological interest are: (I) High-resistivity unsaturated basalts; (II) Seawater intrusion wedge underlying thebrackish basal aquifer; (III) Near-surface, low-resistivity units consisting of colluvial deposits; (IV) Internal, low-resistivity unit of saturated basalts overlying an impermeable stratum.

519N. d'Ozouville et al. / Earth and Planetary Science Letters 269 (2008) 518!522

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Hydro-geomorphological Evolution

Fernandina 2009 Eruption ConeG. Merlen

San Cristobal ravine at coastN. d’Ozouville

d’Ozouville, 2007


Conceptual Age Related: Isabela -> Santa Cruz -> Floreana -> San Cristobal

Phase I: Basal Aquifer + coastal outflowPhase II: Basal Aquifer + cinder cone aquifer + “hidden” high-level aquiferPhase III: Basal Aquifer + cinder cone aquifer + developed drainage networkPhase IV: Basal Aquifer + high-level aquifers + springs + permanent stream network


• Something we’ve thought about ... still a lot missing to go from conceptual model to modeling

- landslides? rates?

• Find a way to integrate a few more scales/axis/gradients

- paleoclimates ?

• Focus on development of impermeable layers

- Paleosols, ash deposits or tuff deposits

Conclusions

• 8 years of work starting in a totally unknown environment -> remote sensing, geophysics, hydrology, geomorphology, hydrogeology, climate, soil

-> linked surface and sub-surface processes to provide a first hydrogeological conceptual model of the islands

• Integrated approach looking at all processes within a given location -> started off on a very experimental and exploratory route

-> now focusing in on quantifying and modeling processes.

• WITH the perspective of doing a lot more!

Starting in a totally unkown environment, with performed:

-> remote sensing of fractures, cones and streams-> field characterisation of streams and springs-> a large 3D grid of resistivity from air-borne TEM survey

We propose a first hydrogeological model of the island

Perspectives-> Execution of drillholes-> Need for long term climatic records, stream monitoring

-> water dating -> tracers-> groundwater discharge-> quantifying rates-> finding the aquitards-> landslides

-> comparing certain processes with those occurring on other ocean islands

d’Ozouville, 2007

Had freshwater been the sole object of our explorations, we would have been indeed empty handed but every time we sailed forth, the resulting treasure of strange beauty and interest almost made us forget that we were thirsty.

Beebe (1924)

Sierra Negra, 23 July 2011

Documents

The Galapagos Islands: a Laboratory for the Study of ...dgeist/Chapman/ChapmandOzo… · • A look at other oceanic islands - • Comparing islands within the archipelago - Tortuga