caldera 
covered by 150- to 250-
m-thick ice (Figure 
1). Its highest peak, Grímsfjall, on the southern 
caldera rim, reaches an elevation of 1722 
m. 
Volcanic eruptions there, numbering several 
per century, are phreatomagmatic because 
of the ice cover, and they usually persist for 
days to weeks. Geothermal activity continu-
ously melts the overlying ice, and meltwater 
accumulates in a subglacial
        
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