Tungurahua Volcano, Ecuador, activity update: increasing explosive activity

Tungurahua's eruption continues. This morning, a tall ash plume was rising to 32,000 ft (ca. 10 km) altitude and drifting west. A slight decrease in tremor is visible on the latest seismograms.
So far, effects of the eruption have been limited to ash fall. In canton Quero, the ash fall during the past days has damaged more than 5000 hectares of plant cultivations and hit about 2.000 families.
In the meanwhile, scientists from the volcano observatory have made an overflight of the volcano and posted the following interesting update (freely translated) for 20-21 Aug:

The volcano emits a neary constant eruption column, associated with explosions, that reached a maximum height of 5 km and an average height of 1.5 km above the crater, with moderate ash content, drifting to the west. There were no new reports of ash fall.
An increase in the number and size of the explosions was observed since 15:00 local time on 20 Aug. Until 16:00 on 21 Aug, there were 16 large explosions producing strong cannon-shot noises heard in villages near the volcano and in cities as far away as Ambato, Riobamba and Miracle.
The seismic activity at Tungurahua shows a constant tremor signal associated with steam, gas and ash emissions.
Otherwise, the roaring noises have decreased in intensity and duration with respect to the previous days.
In the evening observatory staff observed constant expulsion of hot material in jets. Lava blocks landed outside the crater and rolled up to 1.5 km from the top of the volcano's flanks.

An explosion at 14:11 on 21 Aug generated an ash column rising 4 km above the crater, that produced a small pyroclastic flow that descended approximately 2.5 km along the Achupashal creek.

Staff of the Geophysical Institute of the National Polytechnic School conducted an overflight of the volcano yesterday afternoon for thermal and visual monitoring of the activity in the crater area and top of the mountain. They observed that that much of the western and southwestern flank have been covered by fresh ash and blocks.
Thermal images show near continuous explosive activity from the inner crater, ejecting incandescent material onto the the upper flanks of the volcano, where temperatures ranged between 116 and 150°C.

The morphology of the summit consists of an outer crater containing an inner crater about 80 m wide, and a few dozend meters distance from the outside crater. The inner crater was observed to be almost filled with fresh lava. Numerous large meter sized hot blocks could be identified in the crater area and the upper flanks. Temperatures measured at the crater raned between 550°C for the inner crater and 236°C at the outer crater.

Many fresh lava blocks have accumulated in ravines on the south-west, west and north-west upper flanks of the volcano. These could be mobilized to form avalanches IG scientists warn.

The thermal image analysis confirmed that during the night of Saturday, August 18, a lava flow and an incandescent avalanche of blocks that had accumulated in the north-western flank flew down through the Cusu canyon as had been observed then.

IG recommends the authorities and the general public to maintain protective and preparative measures in case the activity escalates further which is a possibility. Most danger during the ongoing activity comes from pyroclastic flows, lahars and ash fall.

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