Although there has been no extrusion of lava since 11 February 2010, scientists at the MVO keep a close eye on the state of dome, looking for changes such as increased rockfall activity, changes in the number and temperature of fumaroles or other general morphological changes caused by erosion. To do this, MVO conducts frequent observation flights, during which photographs and thermal images are acquired, and acquire satellite radar imagery.
Recent photographs and satellite radar images show changes on the dome that are the result of the activity on 4 and 5 February 2013. The activity included volcano-tectonic earthquakes, elevated gas flux and increases in activity at many of the fumaroles located inside the 11 February 2010 collapse scar on the north flank of the volcano. The increased fumarole activity resulted in the formation of a new crater around a prominent fumarole inside the collapse scar (see photo above), as well as the removal of material from around fumaroles near to the summit of the volcano. In the satellite radar image shown to the left, the cyan coloured area marked by arrows shows where the largest changes have occurred. This part of the dome is nearly always covered by cloud, so the radar images provide a very useful view of the dome, even when it can’t be seen from MVO.
In addition to the recent changes inside the 11 February 2010 collapse scar, degradation of the east side of the dome, at the head of the Tar River valley, has continued since extrusion stopped in 2010. On 8 March 2013, scientists observed a large fissure in the cliff in the east side of the dome, part of which has existed since 2007 (see photo to right). The presence of the fissure, parallel to the cliff face and estimated to be 2 m wide, suggests that a large slab is slowing peeling away from the dome. Should this slab fail as a single block, it will likely produce a large pyroclastic flow that would descend the Tar River valley, safely away from any populated areas. The formation of the fissure is a result of slow cooling and subsequent erosion of the dome, a process that will continue for many decades, even after the current eruption is over.
This pyroclastic flow generated a small ash cloud which rose between 3000 and 4000 feet and was carried westward over Plymouth. The flow lasted about 75 seconds and had a runout of about 1-1.5 kilometres with a significant fine-grained surge component (see photo).