The Alaska Volcano Observatory is reporting that both current eruptions in the Aleutians – at Okmok Caldera and Mount Cleveland – are showing signs of a lava extruding from the vent. Thermal anomalies have been imaged at the vents of both volcanoes, although no lava has been seen thus far. Both volcanoes continues to emit ash and steam.
The news that lava is erupting isn’t really shocking (it is a volcano, you know). Many times, these eruptions begin with a “throat-clearing” phase of ash and volcanic debris being erupted from the vent. If the magma is still rising after these initial explosive events, then depending on the composition of the magma/lava, it will make its way to the surface through the vent. Now, as you might imagine, it is difficult to perch yourself near the vent to see the lava when it first erupts, so this is why AVO talks about “thermal anomalies”. With our many “eyes in the sky” (a.k.a. satellites), we can watch for large heat differences on land surfaces – the sort of thing the military uses on spy satellites to look for ships heating up their engines when they’re about to leave port. Now, the ash column, while hot, doesn’t carry the same radiant thermal energy of lava emerging from a vent, so when a large thermal anomaly – let’s say a few hundred degrees – is seen at the volcanic vent, it is a good bet you’re seeing lava coming out (see the image of Augustine Volcano erupting in 2006, above). Whether this means that the eruption is winding down or cranking up, well, that is still anybody’s guess without proper seismic information to go along with the thermal data.