Anak Krakatau volcano (Sunda Stait, Indonesia), activity report
Wednesday Dec 05, 2007 16:15 PM |
During VolcanoDiscovery's expedition, thanks to extraordinary good weather, we were able to observe Anak Krakatau's ongoing eruption during 21-26 November: overall, its activity was relatively constant and ranged from strong strombolian to weak vulcanian activity, probably according to various levels of phreatomagmatic and magmatic activity within the conduit.
All activity occurred from the newly formed crater on the upper southern flank just below the old summit crater of Anak Kraktau. On 21 November, this crater had an oval shape and was approximately 50x70 m in diameter. Reports of lava flows earlier in the course of the eruption could not be verified and no deposits from lava flows were visible, only debris from ejected solid blocks and a few deformed fresh bombs.
The most frequent, typical type of acitivty that was present during most of the time consisted in ash venting. Dense, dark brown brown, billowing ash clouds escaped in pulses from the crater, rose typically 100-200 meter and occurred at near-constant intervals of about 2 minutes. At all times, the ash was drifting east due to near constant westerly winds. Only few or no blocks were observed being ejected along with such ash clouds. On 24 November, we observed phases where ash venting became continous over several minutes.
At more irregular intervals, about 10-30 minutes apart, more violent, small vulcanian-type explosions interrupted the ash venting events. The explosions consisted in a sudden spray of mostly solid rocks and few incandescent scoria, followed by more powerful and turbulent ash plumes, which rose up to above 1 km.
Generally, these vulcanian-type explosions tended to occur after slighly longer repose intervals with no or little visible activity in the crater and in most cases, the length of the repose interval was correlated with the force of the explosion. Several exceptionally powerful explosions occurred at intervals of approximately 16-24 hours: the strongest one occurred happened shortly after midnight on 21-22 November, and showered the whole of Anak Krakatau island with incandescent blocks, ignited bush fires and produced a very loud cannon-shot noise that rattled windows on the west coast 40 km away. Other unusually large blasts occurred at around 2am on 21 Nov, at around 9am and 1:20 pm on 23 November.
Activity shifted temporarily towards more strombolian type explosions on the evening of 22 November: until about 1 am on 23 November, most activity then consisted in bright, scoria-rich strombolian explosions with lots of fresh incandescent bombs that produced only relatively little ash compared to the preivious activity. After some of the more powerful strombolian explosions, we observed weak, near-continuous spattering from a vent in the crater.
Increasing activity after 23 Nov:
Early on 23 November, activity returned to more ash-rich, probably phreatomagmatic in origin, activity. Ash production and the average violence of the individual events increased slighlty but visibly over the next two days, while a rythm of single events at near-constant intervals of about 2 minutes was maintained. During 24-25 November, ash plumes typically rose to >1 km above the crater and were well visible from the west coast.
Photos showing the activity and impressions from the expedition can be found at: www.volcanodiscovery.com/volcano-tours/krakatau/photos.html
Wednesday, Nov 21, 2007
The Strombolian activity of Anak Krakatau is still going on with explosions and incandescence. Lava flows are visible from the islands around Anak Krakatau. The Alert Level remained at ... [more]
Thursday, Nov 15, 2007
Anak Krakatau continues its new strombolian activity from the new vent south of the summit crater. The eruptions are producing small ash plumes, ejections of incandescent spatter bombs as well as lava flows, as news reports and data from KRAKMON indicate. Seismicity was at elevated levels. [more]
Thursday, Nov 08, 2007
There are still ongoing Strombolian eruptions from Anak Krakatau reported. [more]
Wednesday, Oct 31, 2007
GAK published a series of photos showing the new activity at Anak Krakatau. A vent located on the S flank of the summit cone formed as pit crater around 23 October; on around 25 October, phreatic (?) and probably phreatomagmatic ash eruptions started from this location, producing clouds of ash 200-300 m high, and occurring at intervals of 3-6 minutes. [more]
Monday, Oct 29, 2007
Our guide Doni from Indonesia just reported new eruptions at Anak Krakatau and that there are new craters on that volcano island. Also Soputan volcano is getting more active the last days. [more]