amplitude plots for three of the most recent Grímsvötn eruptions,
which occurred on December 18, 1998 (Figure 10a), November 1, 2004 (Figure 10b), and May
21, 2011 (Figure
10c). The station skr is plotted and can thus be compared for all three
eruptions, exhibiting differing types of pre-eruptive tremor signal for each year. The warning
times provided by Tremv-ALERT range between 25 minutes
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