Geothermal activity within the subglacial Katlacaldera, Iceland

Magnús T. Gudmundsson, Þórdís Högnadóttir, Hannah I. Reynolds, Eyjólfur Magnússon

Nordvulk, Institute of Earth Sciences, University of Iceland

GEORG Workshop 25 November 2016

High temperature geothermal areas in Iceland – about one third under ice

Katla caldera• the second largest caldera in Iceland• 100 km2 and up to 700 m deep• Filled with 400-700 m of ice• One of the most dangerous volcanoes in

Iceland• Geothermal activity in many parts of

caldera

From Larsen (2000)

Kjartan Guðmundsson 1918Katla volcano: • Renown for eruptions and • associated jökuhlaups (glacier

outburst floods) • 21 known eruptions since 9th

century AD• Last such event in 1918• Everybody has been waiting since

about 1960 for the next one

Geothermal activity:ice cauldrons formed by basal melting

Two types:• Accumulation of meltwater and

sudden, discrete drainage events• Continuous drainage

Both types observed in Katla

TF-FMS – Isavia survey aircraft

Geothermal activity in Katla

Geophysical signals 1:

Seismic undershooting –shallow magma chamber

(Ólafur Gudmundsson et al., 1994)

Geophysical signals 2:

Aeromagnetic surveyingnon-magnetic body in centreof caldera

(Jónsson and Kristjánsson, 2000)

Geophysical signals 3:

Bouguer anomaly mapping:Large intrusion under caldera –relatively low-density body at shallow depth encircled by highdensity bodies

(Gudmundsson, 1994, Larsen et al., 2013)

Geothermal activity and structure:• Geothermal activity within

caldera• Aligned along caldera rim• Over and near inner margins of

shallow high density bodies• No geothermal activity directly

above the shallow, seismicallyimaged, magma body

Based on:Ó. Gudmundsson et al. 1994Jónsson and Kristjánsson, 2000Larsen et al. 2013Gudmundsson et al., 2007

Variations with time – sudden events - draining of cauldron K16, K9 and K10 in 9 July 2011

Events in 9 July 2011: Sudden flood – drainage of ice cauldrons - bridge destroyed

Chemical analysis of floodwater and cauldron development suggestincreased geothermal activity

9 July 2011

Events in 9 July 2011: Sudden flood – drainage of ice cauldrons - bridge destroyed

Chemical analysis of floodwater and cauldron development suggestincreased geothermal activity

9 July 2011

11 July 2011

Summary:

• Large caldera – geothermal activity correlates withcaldera faults

• Ice cover conceals geothermal areas• Monitoring of cauldrons allows approximate power

estimates• Possible to monitor variations in power• Variations of time scale 1-4 years observed 1999-

2016• Peaks in geothermal activity correlated with other

activity (seismicity, uplift, flooding)