Magmatic Processes in the Eastern Branch of the East African Rift (Kenya/Tanzania) Juliet Biggs 1, Elizabeth Anthony 2 , Cindy Ebinger 3 , Falk Amelung 4 , Noel Gourmelen 4 , Tim Dixon 4 1 ESA STSE Fellow, University of Oxford; 2 University of Texas, El Paso; 3 University of Rochester; 4 University of Miami
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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’
Presenter
Presentation Notes
STOP
• 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
Presenter
Presentation Notes
STOP
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
Presenter
Presentation Notes
STOP
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
Presenter
Presentation Notes
STOP
• 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
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