Glacial Seismic Events
 
Figure 1: Tungnakvíslarjökull outlet glacier in western Mýrdalsjökull glacier.
(Photo: Jósef Hólmjárn)

 
  Research team at Uppsala University (Sweden):

Kristín Jónsdóttir, Roland Roberts, Veijo Pohjola, Björn Lund, Zaher Hossein Shomali, Ari Tryggvason, Reynir Böðvarsson

 

A summary of our study of the Goðabunga long period (lp) seismic events:

Long period (lp) events are often recorded in volcanic environments and have been shown to predict eruptions. The lp events in Goðabunga (western Mýrdalsjökull) have been recorded for decades. The events show a clear seasonal and climate-related correlation where their number increases in the autumn as well as during warmer years, and many of them form groups with very with similar waveforms. New broad-band seismic data collected in 2007 suggests that the lp events originate in a steep outlet glacier of the ice cap Mýrdalsjökull, which covers Katla. Here, ice movement leads to ice falls over the steep escarpment, and we now believe that the lp events are generated by large ice falls moreover they are not related to gas or magma movements within the volcano, and are not precursors to an eruption as previously suspected. This observation probably has major significance for hazard estimation at the many ice-covered volcanoes around the world.

 
Figure 2: A simplified sketch of Tungnakvíslarjökull outlet glacier which falls steeply into a valley west of Mýrdalsjökull. The glacier is viewed from north. The sketch is based on photographs (from Jósef Hómjárn in 2000 and 2002) as well as maps (Landmælingar Íslands).
 

 
Figure 3: From top: Summer (May through August). Water channels are expanding and water runs quickly through the glacier. Low electrical conductivity measured in glacier outlet rivers confirms that. Few lp-events are observed during that period. Middle: Autumn (September through November). Water channels collapse. Heavy rain penetrates through the glacier forming a system of linked cavities. Water runs slowly through the glacier and underlying material and high conductivity is measured. Many lp-events are observed. Bottom: Winter (December through May). No or very little access to water. Few lp-events observed.
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