Magmatic Processes in the Eastern Branch of the East African Rift (Kenya/Tanzania)

Juliet Biggs1,

Elizabeth Anthony2, Cindy Ebinger3, Falk Amelung4, Noel Gourmelen4, Tim Dixon41ESA STSE Fellow, University of Oxford; 2University of Texas, El Paso; 3University of Rochester; 4University of Miami

Mec

hani

sm

Faulting

Magmatic

Age

of R

iftin

g

Immature

Mature

Am

ount

/Rat

e of

Ext

ensi

on

Cru

stal

/Lih

tosp

heric

Thic

knes

s

Thick

Thin

Rift ‘Unzipping’

• At what point does magma become important in rifting?

• How do the systematic variations in geophysical parameters (crustal thickness, magma flux, spreading rate) affect magmatic processes?

Scientific Questions:

Broader Impacts:Geohazards

Geothermal Power

Moment Release

Geodetic

Seismic

M7.2

2005 Dabbahu Event, Afar.

Wright et al, 2006

Lake Natron Event 2007

14th July-6th August (22 days)

57 Earthquakes Mb 3.6-5.9

July 17th

Envisat IS6

July 23rd

Envisat IS2

July 21st

ALOS

Biggs et al, GJI, 2009

Time

Remove shallow graben

Common model elements

Time Sequence

Day 7-: Magma chamber deflation clearly visible.

Day 5-: Dyke continues opening, but does not lengthen.

Days 5-7: Collapse of Shallow Graben

Days 3-5: Dike opening begins

Days 1-3: Fault Slip

Geodetic

Seismic

Moment Release

M7.2

M6.2

Dabbahu, 60 km.

Lake Natron, 10 km.

Spreading Rate (mm/yr)10 20

40

80

Dik

e Le

ngth

(km

)Natron

Dabbahu

Asal Ghoubbet, Afar

Krafla, Iceland

Also:- Cumulative extension- Crustal thickness- Magma flux

Dike Propagation Model (Segall, 2001)

Small, Deep Chamber

Short, buried dyke

Large, Shallow Chamber

Long, shallow dyke

Controlled by 3 lumped parameters: • Magma chamber properties ()• Conduit flow (R)• Driving Pressure ()

Magma Chamber

Conduit

Dike

Thick Crust

Low Magma Flux

TANZANIA AFAR

Thin Crust

High Magma Flux

Namarunu

Emuruangogolak

Silai

Paka

Korosi

Ol Kokwe

Menengai

Eburru

Longonot

Olkaria

Suswa19

97-2

000

2003

-200

620

06-2

008

UpliftSubsidenceNo movement

Kenyan Rift Volcanoes 1997-2008

Kenyan Rift Volcanoes 1997-2008

Suswa2-5 cm down

Menengai2-5 cm down

Paka - 21 cm uplift

Longonot - 9cm uplift

2006-2008: Paka

Uplift

21.3 cm vertical (7 fringes = 19.6 cm los)Date Range (9 months) 29 May 06 - 05 Mar 07

Stack of 5 images

5 km

Depth (km)

Radius (km)

Misfit (mm)

3.5

-

11.7

Mod

elR

esid

ual

Mogi

2.8

6.3

10.5

Pen ny

2006-2008: Paka

Biggs et al, Geology, 2009

Depth (km)

Radius (km)

Volume (m3)

2.8

6.3

150 x 103

Pen ny

Mod

elR

esid

ual

Liquid magma

Volatiles Hydrothermal

What causes the volume change?

Stack of 5 images

5 km

• Active magma systems under several ‘inactive’ rift volcanoes in Kenya.

• Magmatic activity (dikes and magma chambers) occur in both mature (Afar) and immature (Tanzania) sections of the East African rift.

• Dike properties are influenced by systematic variations in geophysical parameters along rift.

Conclusions

Continuing work as part of ‘ESA Changing Earth Science Network’

Kenyan Rift Volcanoes 1997-2008

Magma Chamber

To make a dike ~10 times longer in Afar:

Increase chamber volume by 100,

Decrease chamber depth by ~ 5.

Or a combination of both….

Dabbahu,

= 0.1; Natron,

= 10.

i.e long dikes require large, shallow chambers