Krakatau volcano (Indonesia) Nov 2018 eruption: vulcanian activity

During 20-21 Nov, activity changes significantly: explosions became more rich in ash and contained much less and much less brighter lava bombs. As well, the intervals between individual events gradually increased overall, reaching up to about 2 hours by 22 Nov afternoon although phases of more frequent activity still occurred.
The most likely cause is that the magma column continued to drop internally and thus favored the formation of a more robust blockage, which in turn favored the occurrence of strong vulcanian-style explosions with less fresh incandescent material, but many fragments of the plug. This process is possibly helped at depth by water seeping into the walls of the conduit (so-called phreatomagmatic activity) as the interior pressure dropped.
Visible activity almost completely ceased during the night 22-23 Nov and picked up only again in the afternoon of 24 Nov, when we saw it from the volcano observatory on our way back.
Small, ash-rich explosion on the afternoon of 20 Nov. (Photo: Tom Pfeiffer)
Small, ash-rich explosion on the afternoon of 20 Nov. (Photo: Tom Pfeiffer) [info]
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Ash plume from the same explosion a few seconds later. (Photo: Tom Pfeiffer)
Ash plume from the same explosion a few seconds later. (Photo: Tom Pfeiffer) [info]
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Beginning of a small explosion. Compared to the previous day, only few bombs are incandescent. (Photo: Tom Pfeiffer)
Beginning of a small explosion. Compared to the previous day, only few bombs are incandescent. (Phot... [info]
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Dark bombs falling out of the ash plume. (Photo: Tom Pfeiffer)
Dark bombs falling out of the ash plume. (Photo: Tom Pfeiffer) [info]
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An eruption seem from 800 m distance. (Photo: Tom Pfeiffer)
An eruption seem from 800 m distance. (Photo: Tom Pfeiffer) [info]
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A large glowing block about to land on the slope of the cone. (Photo: Tom Pfeiffer)
A large glowing block about to land on the slope of the cone. (Photo: Tom Pfeiffer) [info]
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Ash-rich explosion with two large bombs leaving the eruption column on parabolic paths. (Photo: Tom Pfeiffer)
Ash-rich explosion with two large bombs leaving the eruption column on parabolic paths. (Photo: Tom ... [info]
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Base of the ash column during the eruption. (Photo: Tom Pfeiffer)
Base of the ash column during the eruption. (Photo: Tom Pfeiffer) [info]
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Small vulcanian explosion seen from Rakata (night 20-21 Nov) (Photo: Tom Pfeiffer)
Small vulcanian explosion seen from Rakata (night 20-21 Nov) (Photo: Tom Pfeiffer) [info]
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A moderately strong explosion early on 21 Nov. (Photo: Tom Pfeiffer)
A moderately strong explosion early on 21 Nov. (Photo: Tom Pfeiffer) [info]
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A strong explosion in the morning of 21 Nov: the absence of wind today lets the ash plume rise vertically to approx. 1.5 km altitude. (Photo: Tom Pfeiffer)
A strong explosion in the morning of 21 Nov: the absence of wind today lets the ash plume rise verti... [info]
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Since the early morning of 21 Nov, the frequency and style of eruptions has changed: intervals are sometimes more than an hour. (Photo: Tom Pfeiffer)
Since the early morning of 21 Nov, the frequency and style of eruptions has changed: intervals are s... [info]
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Ash column rising vertically from the crater. (Photo: Tom Pfeiffer)
Ash column rising vertically from the crater. (Photo: Tom Pfeiffer) [info]
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Patrick taking a swim while a vulcanian explosion occurs around noon. (Photo: Tom Pfeiffer)
Patrick taking a swim while a vulcanian explosion occurs around noon. (Photo: Tom Pfeiffer) [info]
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In the evening, the eruptions are again a bit smaller and more frequent. (Photo: Tom Pfeiffer)
In the evening, the eruptions are again a bit smaller and more frequent. (Photo: Tom Pfeiffer) [info]
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The eruptions are all very rich in ash and contain much less of glowing material (compared to the days before). (Photo: Tom Pfeiffer)
The eruptions are all very rich in ash and contain much less of glowing material (compared to the da... [info]
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Incandescent jet of ash and small bombs. (Photo: Tom Pfeiffer)
Incandescent jet of ash and small bombs. (Photo: Tom Pfeiffer) [info]
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Dark ash with embedded glowing material is ejected in the blue hour. (Photo: Tom Pfeiffer)
Dark ash with embedded glowing material is ejected in the blue hour. (Photo: Tom Pfeiffer) [info]
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Small and brighter eruption after nightfall, but with full moon. (Photo: Tom Pfeiffer)
Small and brighter eruption after nightfall, but with full moon. (Photo: Tom Pfeiffer) [info]
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A moderately strong eruption seen from Anak Krakatau. (Photo: Tom Pfeiffer)
A moderately strong eruption seen from Anak Krakatau. (Photo: Tom Pfeiffer) [info]
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Small lightnings occur sometimes. (Photo: Tom Pfeiffer)
Small lightnings occur sometimes. (Photo: Tom Pfeiffer) [info]
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Small eruption with the blue night sky. (Photo: Tom Pfeiffer)
Small eruption with the blue night sky. (Photo: Tom Pfeiffer) [info]
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Suddenly, a stronger explosion fills the full format frame pointed towards the upper part of the cone. (Photo: Tom Pfeiffer)
Suddenly, a stronger explosion fills the full format frame pointed towards the upper part of the con... [info]
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A very large bomb has disintegrated into a trail of glowing rock fragments sliding down the slope. (Photo: Tom Pfeiffer)
A very large bomb has disintegrated into a trail of glowing rock fragments sliding down the slope. (... [info]
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A second powerful eruption occurs about 10 minutes later. (Photo: Tom Pfeiffer)
A second powerful eruption occurs about 10 minutes later. (Photo: Tom Pfeiffer) [info]
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Ash plume rising from the eruption in the previous picture. (Photo: Tom Pfeiffer)
Ash plume rising from the eruption in the previous picture. (Photo: Tom Pfeiffer) [info]
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During the rest of the night, mostly smaller eruptions occur. (Photo: Tom Pfeiffer)
During the rest of the night, mostly smaller eruptions occur. (Photo: Tom Pfeiffer) [info]
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Ash venting at night. (Photo: Tom Pfeiffer)
Ash venting at night. (Photo: Tom Pfeiffer) [info]
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A phase of strombolian-type activity lasts about a quarter of an hour. (Photo: Tom Pfeiffer)
A phase of strombolian-type activity lasts about a quarter of an hour. (Photo: Tom Pfeiffer) [info]
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During the night 21-22 Nov, a few moderately large explosions occur. (Photo: Tom Pfeiffer)
During the night 21-22 Nov, a few moderately large explosions occur. (Photo: Tom Pfeiffer) [info]
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These vulcanian-type eruptions typically produce ash plumes that rise 1-2 km and eject lots of material suddenly, but only comparably few glowing lava rocks. (Photo: Tom Pfeiffer)
These vulcanian-type eruptions typically produce ash plumes that rise 1-2 km and eject lots of mater... [info]
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Eruption in the morning of 22 Nov. (Photo: Tom Pfeiffer)
Eruption in the morning of 22 Nov. (Photo: Tom Pfeiffer) [info]
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Generally, the activity has changed a lot by 22 Nov. Longer phases of quiet occur, typically followed by moderate to strong vulcanian explosions. (Photo: Tom Pfeiffer)
Generally, the activity has changed a lot by 22 Nov. Longer phases of quiet occur, typically followe... [info]
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A stronger vulcanian explosion sends many blocks behind the old crater rim (lower right in image). (Photo: Tom Pfeiffer)
A stronger vulcanian explosion sends many blocks behind the old crater rim (lower right in image). (... [info]
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Bombs landing on the southeastern flank of Anak Krakatau, whirling up dust. (Photo: Tom Pfeiffer)
Bombs landing on the southeastern flank of Anak Krakatau, whirling up dust. (Photo: Tom Pfeiffer) [info]
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A small eruption in the afternoon. (Photo: Tom Pfeiffer)
A small eruption in the afternoon. (Photo: Tom Pfeiffer) [info]
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