Tracking melt injection under the Mid-Atlantic Rift near Askja, central Iceland

Lead Research Organisation: University of Cambridge
Department Name: Earth Sciences


The crust of the large oceanic island of Iceland in the North Atlantic is formed almost entirely from successive volcanic eruptions which fill the gap caused by the separation (rifting) of the plates on which North America and Europe sit. The massive volcanism in Iceland is caused by the deep mantle there being hotter than normal, and so melting more than normal to produce large amounts of molten rock, or magma. Although the melt is formed in the deep mantle at depths of 40-100 kilometres, it is very buoyant and bleeds rapidly up towards the surface. Normally it ponds in the crust in a magma chamber about 5-6 kilometres beneath the surface until a sufficiently large volume has built up to cause an eruption. Our main objective is to investigate some exceptionally deep earthquakes occurring 15-30 kilometres beneath the surface under the active volcanic system of Askja in central Iceland. These occur at depths where the crust should be hot enough to prevent brittle failure generating any earthquakes. We first discovered these deep earthquakes in summer 2006, and will now target an array of seismometers specifically to investigate them further. Our hypothesis is that they are caused by melt moving in the deep crust. This is an exciting observation, since such deep earthquakes have only rarely been observed before, and never in a rift zone; it means that we can catch the volcano in the act of transferring molten rock through the crust. A second objective is to monitor a new area of activity, again thought to be caused by melt injection, which started in February 2007 beneath a previously seismically quiet area on the edge of the rift zone some 20 km east of Askja. Over 3000 events have occurred up to mid-August 2007, gradually decreasing in depth from 20 to 15 km and latterly extending almost to the surface. This may represent injection of molten rock into a shallow magma chamber which may result in a volcanic eruption. Previous experience suggests that activity is likely to persist for around 2 years, so we have an opportunity to track almost the entire development of a melt injection (and possibly eruption) episode. Thirdly we will map the location of the underground storage reservoirs (magma chambers), by using the fact that the crust above them is cold and brittle, therefore allowing numerous small earthquakes to occur as it fractures, whereas the hot magma chambers deform ductilely without fracturing. So by mapping where the earthquakes are absent, or where seismic waves are absorbed by passing through rock containing some melt, or rock at high temperatures, we can map the region of the magma chamber. Our seismic data will also be used to calculate the crustal thickness in this region, which is presently poorly known. Results form our studies will be integrated with information from other researchers investigating deformation in the region using satellite measurements which can detect motions at a millimetre scale, together with surface mapping of faults in the crust and evidence from detailed petrological studies of the rocks which provide control on the depths at which the molten rock has ponded in the crust during its ascent to the surface. The Askja area is inhospitable, and is easily accessible only in the summer months of July-August when snow is absent. Winter temperatures plummet to -25C. We shall install our seismometer array during summer 2008, but leave them operating remotely through the winter to gain a complete picture of the seismicity through time. The seismometers include a satellite clock receiver which provides accurately timing. Solar panels with large batteries will power the instruments through the dark winter months. Data from one of the stations will be radio-telemetered to Reykjavik and hence accessible via the internet from Cambridge, while the remainder will record data internally, to be collected in summer 2009.


10 25 50
Description We have mapped hundreds of tiny earthquakes at depths of 12-25 km beneath the Askja rift segment in central Iceland. Normally there are no earthquakes at this depth in the crust. We attribute these micro-earthquakes to molten rock forcing its way up in the crust. Because the molten rock is formed at great depths of 40-100 km beneath the surface, it has to force its way upwards before it can erupt. We have caught it in the act of doing so, in several specific locations near the volcano.
Exploitation Route These results are of importance in understanding how volcanoes are replenished with molten rock. Since volcanoes only erupt sporadically, it may also help with eruption forecasting if there can be seen to be an increase in melt movement beneath a volcano.
Sectors Aerospace, Defence and Marine,Environment

Description NERC REsearch Grant
Amount £469,578 (GBP)
Funding ID NE/H025006/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 01/2011 
End 12/2014