Eruption in Eyjafjallajökull
Eruption update 21 April
Eruption continues with less explosive activity. Eruption rate is inferred to have declined over last few days and now be an order of magnitude
smaller than during the initial 72 hours of the eruption. Present eruption rate is estimated to less than 30 m3/s of magma, or 75 tonnes/s , with a
Eruptive style: The northernmost one of two main craters in the summit caldera is active. Phreatomatic explosive activity occurs with some lava
spatter at craters.
Plume height: about 3 km
Tephra dispersal: local towards the south
Meltwater: minor, but what is melted flows down into Markarfljót, no signs of water accumulation in craters
Seismic tremor recorded by the Icelandic Meteorological Office: some fluctuations but mostly stable. Tremor is not decreasing and does not reflect the
decline as inferred for the eruption rate.
GPS-measurements: indicate continuing small pressure decrease under the volcano at a similar rate.
Composition of erupted material: Samples collected April 19 show same composition as early in the explosive phase, but fluorine content is higher.
Samples collected 19 April have 850 mg/kg (initially it was 25-35 mg/kg). This is due to the change in eruptive style – tephra is now not washed to
the same extent by water in the eruptive plume.
Amount of erupted material: Uncertain but on the order of 100 millon cubic meters. Tephra next to craters is 20-30 m thick.
Compiled by: Freysteinn Sigmundsson, Magnús Tumi Guðmundsson, Guðrún Larsen, Níels Óskarsson, Sigurður Reynir Gíslason, Páll Einarsson,
Sigrún Hreinsdóttir, Rikke Pedersen, Ármann Höskuldsson, Guðrún Sverrisdóttir, other staff of Institute of Earth Sciences and collaborators.