I spent over a month working in Indonesia a little over a year ago, and was again impressed with the country's beauty and variety of its volcanoes. Indonesia has over 100 "active" volcanoes (those that have erupted in historical time and have the potential to erupt again), and typically 6-10 of them erupt each year! Two of them (SINABUNG and KELUT) have been in the news lately and are worth describing.
[Late March, 2014] Sinabung continues to erupt - here is the latest report from the Volcanological Survey of Indonesia (as quoted by the Smithsonian/USGS Weekly Report):
"Activity at Sinabung during 15-22
March is based on observations from a post in the Ndokum Siroga village,
8.5 km away. Dense white plumes rose 500 m above the lava dome daily,
and as high as 1 km on 21 March. Lava had traveled
2.4 km down the flanks as of 20 March and was incandescent at various
areas. Incandescent material originating from the edges of the lava dome
and flow traveled up to 1.5 km S and 200 m SE. A pyroclastic flow
traveled 3 km S on 17 March. Tremor and volcanic
earthquakes were detected, and signals representing avalanches from the
unstable and still-growing dome decreased slightly. Sulfur dioxide
emissions varied between 300 and 598 tons per day, indicating no new
magma. The Alert Level remained at 4 (on a scale
of 1-4). Visitors and tourists were prohibited from approaching the
crater within a radius of 5 km."
SINABUNG is an isolated, small stratovolcano located near the gigantic Toba caldera - site of one of the world's most powerful "super eruptions" 75,000 years ago (VOLCANOES-Global Perspectives, p. 259). This area is relatively sparsely populated, although nonetheless about 30,000 people have been evacuated from surrounding villages since Sinabung's current eruption began in 2010. 17 people have been killed so far by pyroclastic flows from this eruption - mostly because they returned too soon to their evacuated homes. Eruptions are rare on Sumatra, and it is interesting to speculate if this eruption is in some way related to the tectonic forces that caused the great Sumatra earthquake in 2004?
KELUT (or Kelud), in densely populated eastern Java, is one of Indonesia's most deadly volcanoes, and eruptions have killed more than 3,000 people in its 1,000 year recorded history - mostly by lahars that resulted from eruptions that ejected mud and ash from a central crater lake. That lake was displaced by a growing lava dome in 2007, and the volcano had remained quiet until 13 February of this year, when increasing seismic activity prompted the Volcanological Survey of Indonesia to issue a Stage IV Alert and to begin the evacuation of people in the danger zone. Eventually more than 100,000 people were evacuated, but to the credit of VSI, only 5 lives have been lost. Ash rose to 17 km above Kelut, and about 50 million m^
3 of volcanic ash was erupted. The explosive phases of this eruption were short-lived, the Alert level has been lowered to Level 2 (warning), and people are being allowed to return to their ash-buried homes and rice fields.
Volcano Thought of the Month
It is becoming
increasingly clear that the magma reservoirs underlying the world’s active
volcanoes are, for the most part, in a delicate state of gravitational equilibrium
with enclosing rocks, and that many factors can contribute to their destabilization
and to subsequent eruptive activity.Eruption
“triggers” are mostly related to processes that increase the buoyancy and
mobility of magma bodies underlying volcanoes, and in many cases where long
inactive volcanoes erupt, the renewed activity has been shown to be related to
the ascent of new basaltic magma from below (as at Mt. Pinatubo in 1991).
New Book Available!
VOLCANOES - Global Perspectives
About the book: Volcanoes are essential elements in the delicate global balance of elemental forces that govern both the dynamic evolution of the Earth and the nature of Life itself. Without volcanic activity, life as we know it would not exist on our planet. Although beautiful to behold, volcanoes are also potentially destructive, and understanding their nature is critical to prevent major loss of life in the future. VOLCANOES is available in both hardbound (library) and softbound (student) editions. Please let me know of any needed corrections (jplockwood (at) volcanologist.com - MAHALO!