Ground deformation 2012-2015 in the Hengill geothermal area

Daniel Juncu¹, Thóra Árnadóttir¹, Andy Hooper², Gunnar Gunnarsson³

¹Nordic Volcanological Center, Instiute of Earth Sciences, University of Iceland

²COMET, School of Earth and Environment, University of Leeds

³OR – Reykjavik Energy

The Hengill area

• 2 power plants

Nesjavellir operating since 1990–

– Hellisheidi operating since 2006

• Volcanic history

–

–

Last eruption ca. 2000 years BP

Intense seismic activity and uplift 1994-1998

• Plate junction

– Intersection of Reykjanes Ridge, South

Iceland Seismic Zone and Western Volcanic

Zone

Measuring ground

motion• GPS

–

–

61 campaign stations measured

annually by IES and in 2012 by ÍSOR

5 continuous stations operated by IMO

• InSAR

–

–

TerraSAR-X

Between 1-3 images per year of the

whole area

Surface velocities 2012-2015

Correction for

plate motion after

Árnadóttir et al.

(2009)

Subsidence in geothermal areas: ΔP or ΔT?

Modelling the deformation

•

•

Elastic half-space models to

simulate the elastic response of

the rock to pressure change

Fix observed ΔP and use non-

linear optimization to find the

remaining source parameters

Yang et al. (1988)

Results

•

•

Hellisheidi: ~ 0.5 – 3 km depth

Nesjavellir: ~ 1 – 3 km depth

Contraction source in eastern

Hengill: ~7 km depth

Summary

• Hellisheidi and Nesjavellir subside ~1-2 cm/yr

• Observed pressure decrease can explain the

surface deformation

• Regional deformation has to be taken into

account

Takk!