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September 1, 2010 / Dave Gorham

Sinabung: More to Come?

We spoke with ImpactWeather Meteorologist and in-house Geologist Fred Schmude last week about the pending eruption of Mt. Galeras in Colombia. While we wait for Galeras, Mt. Sinabung has jumped into the fray. Once again, Fred Schmude:

There has been a lot of recent news about Mount Sinabung on the Island of Sumatra in the eastern Indian Ocean, which surprisingly erupted after nearly 400 years of dormancy. Several shallow earthquakes occurred near the mountain slope last week followed by a quick blast of ash and rock fragments that reached up to 5,000 feet above the volcano last weekend. Typically shallow earthquakes located underneath a volcano indicate that magma is on the move and depending on the frequency of these quakes volcanologists can determine if an eruption is imminent. In Sinabung’s case there was real no warning other than a few small quakes followed by a quick supersonic rush of ash, rock fragments and gas into the atmosphere.

Mt. Sinabung erupts Monday, August 30, 2010. Image: Sutanta Aditya / AFP - Getty Images

Mount Sinabung is located on the western Pacific Ring of Fire, which is a continuous string of volcanoes stretching around the Pacific Ocean from Asia and Australia on the west side to North and South America on the east side. The reason for all of the volcanic activity is due to geologic plates colliding with one another resulting in long stretches of subduction, with geologic plates sliding under one another resulting in friction, heat and melting of rock.  The melting rock becomes lighter than the surrounding rock, rises and eventually reaches the surface of the earth with time; an erupting volcano is the result. Mount Sinabung stands at 2460 meters (~8,071 feet) and is located on a subducting plate on the island of Sumatra, which is known for many more volcanoes — some of which have erupted very violently in the past.

The reason we are concerned about Sinabung is due to some of the geologic facts about this volcano. First, Sinabung is considered a stratovolcano with steep sides composed of alternating layers of lava flows and pyroclastic flows. Stratovolcanos typically are explosive and can produce very violent eruptions over periods of months and years.  Examples of recent stratovolcanos include Mount Saint Helens in western Washington State, Mount Eyjaffjall over southern Iceland and Mount Etna over Europe, which has had alternating eruptive phases over the past several years. Secondly, there has been little activity on this volcano during the past 400 years, meaning this volcano has had plenty of time to build up pressure, which may eventually lead to a much more violent eruption in the near future. More than likely this is the largest concern for volcanologists right now and one of the main reasons why nearly 30,000 people near the volcano have been evacuated as a precaution for another potentially larger explosion. Thirdly, the magma (molten rock) has large quantities of silica and aluminum, which usually indicate magma that is more viscous and more apt to build up pressure and explode. Finally, Sinabung is in a region of the world known for very violent volcanic eruptions, and its only common sense to assume Sinabung has a similar potential.

For now it’s a wait and see game, not only for the scientists closely monitoring the volcano, but more importantly for the people desperately wanting to return to their homes and farms located on the fertile slopes of the volcano. We may see this concern linger on for weeks and months before we know for sure if the volcano will return to dormancy or enter a much more active phase of activity.  The latter scenario is, of course, our greatest fear.

Scenic Mt. Sinabung under blue sky. Image: Wikipedia

You can read more of our YWB volcano postings here, here and here.


One Comment

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  1. Gavin O'Brien / Sep 1 2010 3:06 PM

    These types of Volcanoes are particularly dangerous. It is to be hoped that people are evacuated from its slopes soon or there may be great loss of life from pyroclastic flows. There are some other Volcanoes in the area which have had nasty eruptions in the past so Sinabung may put on quite an impressive show like the AD 79 eruption of Vesuvius or maybe as big as Tambora (1815)

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