Tungurahua volcano (Ecuador): new eruption
The Tungurahua volcano Observatory while unable to make direct visual observations received reports from observers that fine black ash fell in Pungal and Penipe, and minor amounts in Palictahua. The black color of the ash suggests that it originates from fresh (so called juvenile) magma.
The last eruptive phase of Tungurahua was between 6 Oct and 13 Nov past year and consisted in strombolian-vulcanian explosions generating ash columns rising up to 4 km, accompanied by strong shock waves and producing occasional pyroclastic flows. Bursts of moderate to strong intensity tremor characterized seismic activity during that period.
Since 13 Nov, activity had decreased markedly and the volcano only showed weak degassing and no signs that could have been interpreted as precursors to the current new activity, IGPEN mentions in its latest bulletin.
This implies that the magma that started the current new phase of activity has risen very quickly from a deeper reservoir into the shallow plumbing system of the volcano. In other words, eruptions at Tungurahua can start with little or even no warning.
Sinabung volcano (Sumatra) - continuing lava effusion forms large lava lobe and pyroclastic flows
The sticky lava flow followed and almost completely filled the deep ravine on the SE side of the volcano which before channeled the rockfalls and pyroclastic flows.
However, this steep, blocky lava flow is highly unstable. Collapsing material from the flow still generates frequent rock avalanches and sometimes pyroclastic flows, although the latter ones have been significantly smaller in size than those during late Dec until mid January.
This suggests that the arriving magma is already more degassed and less prone to fragmentation, i.e. explosive activity and pyroclastic flows.
Another significant difference is the changed geometry of the crater and the lava dome. Until 10-11 January, the dome had been confined inside a circular crater with steep outer slopes, which forced all overspilling lava to break apart from the main mass to disintegrate (and partially explode due to gas contained in the lava) into the frequent pyroclastic flows (as opposed to a coherent lobe as now).
This changed probably during the night of 10-11 January, when a major collapse or a sequence of collapse events occurred. It resulted in the formation of the large V-shaped crater breach and the removal of much of the lava dome. A deep canyon starting at the breached crater channeled from then on all rockfalls and pyroclastic flows. The formation of this lower-lying and increasingly eroded "outlet" for the sticky lava also made for an overall less steep path.
Blog Culture Volcan has posted a beautiful description with comparative photos illustrating this evolution of the crater geometry during January.
In combination with a currently less gas-rich (and less prone to explode) magma, the changed geometry allowed the viscous lava from the dome to remain coherent and flow out as a lobe. For the time being, this means that the eruption is in a more stable phase and less dangerous (as pyroclastic flows although they still occurring are less likely).
It is impossible to predict how the eruption will continue. It could come to an gradual end with slowly decreasing lava effusion, but it could also enter a new phase of more explosive activity, if new batches of fresh, gas-rich magma arrive at the summit. As it continues to grow, the risk of a major collapse of the dome and even the lava lobe remains as well.
The situation of the evacuees (about 30,000 according to official numbers) remains difficult. The Indonesian president visited the site last week and promised help and announced that the area in a 3 km radius around the volcano should remain as a permanently depopulated area.
314 years ago Sunday, a megathrust earthquake devastated the region … ready for another?
Posted by James Smith on January 29, 2014
Digging into the soil at the Effingham Inlet in British Columbia, Canadian scientists have confirmed that a city-destroying megathrust earthquake in the Northwest is due.