Mount Sinabung Is Causing Trouble On Sumatra

A quiet Mount Sinabung in 2009.  (Source)

A quiet Mount Sinabung in 2009. (Source: Mike)


Its natural beauty is breathtaking, but folks have to be tough and resourceful to live on the tropical Indonesian island of Sumatra.

Part of the Sunda Arc, Sumatra sits in a subduction zone that’s prone to those dreaded megathrust earthquakes. You might recall the one that happened on December 26, 2004.

Human history

Despite such disasters, some 50 million people do live on Sumatra now, a little over 20% of Indonesia’s total population – it works out to about 96 people per km2.

Why do they stay? Because, even with its geologic dangers, Sumatra has always been a good place to live.

The spice and opium trade put it on the world map – its rich volcanic soil is perfect for agriculture and plantations. Locally, it’s been known since ancient times as the “land of gold” because of deposits of this and other minerals in the volcanic highlands along the west coast.

Plate tectonics underlies Sumatra's earthquakes and volcanoes.  (Source)

Plate tectonics is responsible for Sumatra’s earthquakes and volcanoes. (Source)

About those volcanoes, though…

Mount Sinabung

Gunung Sinabung is one of many (34, by this count) active volcanoes that sit on the western side of the island. One of them, Toba, is a bona fide supervolcano.**

Don’t worry.  Toba isn’t showing any worrisome signs, which is a good thing. Its last eruption, some 74,000 years ago, was the largest one known for the last 2.5 million years.

Today Toba’s caldera is filled with a beautiful lake. It’s a popular tourist destination and home to indigenous peoples as well as many small Indonesian villages.

What an event that may or may not have almost wiped out the human race looks like today. (Image:  Pasadena12)

Toba is strangely beautiful for something that may or may not have almost wiped out the human race. (Image: Pasadena12)

Its neighbor, Mount Sinabung (not shown above), sits some 25 miles from the northern tip of the Toba caldera.

According to research by these Japanese scientists (PDF), the much smaller volcano formed after Toba’s supereruption – hey, on Sumatra, with the Sunda/Java Trench nearby, there’s plenty of magma to go around!

Volcano Emergency Management

Sinabung is a good example of how much we do and do not know about volcanoes. As well, given its location near quiescent Toba, it’s also a good symbol of how volcanoes that aren’t “super” can still “nickel-and-dime” you into a crisis surprisingly quickly.

Let’s look at its recent history and how the Indonesians responded.

When Sinabung cleared its throat in 2010, it caught the country’s disaster management officials at the BNPB – and the VSI volcanologists (Indonesian language) who advise them – by surprise.

They couldn’t really be criticized for that. Because it hadn’t erupted for centuries, Sinabung was a “B” volcano (Indonesian) – only category “A” volcanoes require intensive monitoring (source).

A country with that many volcanoes just cannot keep a monitoring network on each and every one.

Indeed, per the Smithsonian’s Global Volcanism Program experts, Mount Sinabung hadn’t had a confirmed eruption in historical times – just a little fumarolic activity in 1912 that amounted to nothing.


Villages encroach on Sinabung in 2003, during the volcano's long sleep.  (NASA - click to enlarge)

Mankind encroaches on Sinabung in 2003, during the volcano’s long sleep. (NASA. Note: The full 4-MB image includes part of Lake Toba)

I’ve added some links to the history the Smithsonian gives for Sinabung:

Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical, 2460-m-high andesitic-to-dacitic volcano is at the southern end of the four overlapping summit craters. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks of Sinabung in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

This 2013/2014 eruption photo shows the multiple-crater summit elongation nicely.  (Image:  Karo District)

This 2013/2014 eruption photo shows Sinabung’s multiple-crater summit elongation nicely. (Image: Karo District [Indonesian])

The VEI 2 eruption that started at Sinabung on August 27, 2010, may have caught residents and authorities off guard at first, but they quickly responded.

Of course there were mass evacuations. The government also issued the highest warning level for Sinabung in 2010, as the eruption style of this Category B volcano was unknown.

Scientists can’t see into the Earth, so they must install expensive monitoring equipment on a suspect volcano to detect the movement of magma underground and as it approaches the surface.

If there is no historical record, the scientists also need to do ground surveys to find evidence of what has happened there in the past.

The classic example of this process is Mount Pinatubo in the Philippines. You might have watched it play out in Nova’s 1992 “In The Path Of A Killer Volcano” or read about it in Dick Thompson’s Volcano Cowboys: The Rocky Evolution of a Dangerous Science (2000).

Kelut's lava dome in 2007.  These form because volcanoes like Kelud and Sinabung have "sticky" lava, not "runny" like the lava in Hawaii.  (Image:  Volcano Discovery)

Kelud’s lava dome in 2007. Such domes form because volcanoes like Kelud and Sinabung have “sticky” lava, not “runny” lava like the kind in Hawaii. (Image: Volcano Discovery)

A 21st century example in Indonesia is the 2007 eruption of a category A volcano – Kelud on the neighboring island of Java.

Kelud has had over 30 eruptions since 1000 AD, per Wikipedia; during the 20th century alone, it killed over 5000 people, most of them during a lahar in 1919. It also has a history of explosive eruptions.

When it started rumbling in the fall of 2007, therefore, disaster management authorities “put into practice lessons learned from the December 2004 tsunami and from 1990, when Mt Kelud last erupted, killing 35 residents, destroying houses and cropland and covering much of the immediate area in up to 70 centimetres of ash” (source: United Nations).

The eruption of Kelud was a full-scale disaster preparedness test. Some 22,000 people were evacuated fairly smoothly to local shelters. Medical teams went into the region and stayed for the duration, working with regional and national organizations.

The 2007 emergency at Kelud was brief, fortunately, and its management was successful. The head of the district disaster management operation was quoted by the UN source linked above as saying, “We had long been planning for an eruption and were well prepared.”

On Sumatra, they were not as well prepared initially when Mount Sinabung began a series of eruptions in 2010, but as mentioned they made up for it quickly. Indonesians do not mess around when a volcano erupts.

Sinabung erupting in 2010.  (Source)

Sinabung erupting in 2010. (Source)

With the high-level warning in place, authorities ultimately evacuated some 20,000 people to shelters where they received food and masks. The Health Ministry and the Indonesian Red Cross sent doctors and medicine into the region.

Sinabung quieted down after a couple of months. One person had died, a result of respiratory problems while evacuating; the total number of fatalities, per some reports, was two.

While there was some damage, people were able to return to their homes and get on with their lives again.

Overall, the episode had about as happy an ending as can be expected for a volcanic eruption. Scholars intensified their studies of Category A Sinabung after the 2010 eruption, unaware that the Earth was still following its own agenda many miles below their feet.

The Current Volcanic Crisis

On September 15, 2013, at around 3 a.m., Mount Sinabung erupted again. A 3-km evacuation zone was set up and more than 3700 people were evacuated.

It was only the beginning.

A pyroclastic flow down Gunung Sinabung at the end of December 2013.  Note the fields below it - they have since disappeared. (Image:  Karo District [Indonesian])

A pyroclastic flow down Gunung Sinabung at the end of December 2013. Note the fields below it – they have since disappeared. (Image: Karo District [Indonesian])

This time, the eruption continued and gradually intensified.

In November, pyroclastic flows were seen. These started happening more frequently, and a lava dome was noted at the summit near the end of December.

The Indonesian Volcanological Survey (VSI) went to red alert and extended the evacuation zone to 5 km. Soon, some 20,000 people were crowded into area shelters.

As the number of pyroclastic flows increased (with 30 occurring on January 4th!), more and more people were evacuated, although the 5-km zone was maintained.

The rate of flows increased dramatically from January 4th to 5th. Then, on January 6th, a single flow engulfed almost the entire southeastern slope and ran out to 4.5 km. The exclusion zone there was extended to 7 km. By now some shelters were requesting aid from hospitals equipped to handle burn victims (Indonesian).

That said, the evacuations saved many lives. There have been 20 deaths (Indonesian) in the shelters to date, but 19 of those were from illness rather than a direct result of Sinabung’s erupsi (“eruption” – it’s the one word of Indonesian I’ve learned while trying to follow the latest on Twitter). A 19-year-old man is said to have died of “traumakapitis” – your guess is as good as mine.

After that, well…here’s the list of daily events last week from VSI (per Google Translate):

  • Dated January 10, 2014; Earthquake Eruption 38 times, 34 times avalanches…
  • Dated January 11, 2014; Earthquake Eruption 31 times, 214 times avalanches…
  • Dated January 12, 2014; Earthquake Eruption 21 times, 204 times avalanches…
  • Dated January 13, 2014; Earthquake Eruption 10 times, 199 times avalanches…
  • Dated January 14, 2014; Earthquake Eruption 64 times, 201 times avalanches…
  • Dated January 15, 2014; Earthquake Eruption 31 times, 141 times avalanches…
  • Dated January 16, 2014; Earthquake Eruption 57 times, 238 times avalanches…
  • Dated January 17, 2014 (until around 00-06 pm); 6 times Earthquakes eruption, earthquake avalanches 12 times…


Of course you've seen this image in the news, but there are 29 other great images of the Sinabung eruption at "The Atlantic" that accompany it.

Of course you’ve seen this, but 29 other great images of the Sinabung eruption accompany it at “The Atlantic”.

It was on the 15th that I wrote a post about the day’s scary image on the cam and promised that today’s Sunday volcano would be Sinabung.

As of today (Indonesian), Karo District reports there are 28,221 people in shelters, up from 27,671 yesterday. There have been over 1000 medical cases seen. Many necessities appear to be in short supply (Indonesian).

Indonesia’s emergency management system on Sumatra is being strained to and probably beyond its limits.

And the volcano? Well, per John Seach of Volcano Discovery today, the eruption continues with no clear trend.

About an hour ago, as I write this, James Reynolds, who is now watching at Sinabung, tweeted:

Oh, and the rainy season is arriving.

I don’t know what this VSI hazard map for Sinabung says, but most definitely those streams marked in yellow are going to be seeing some heavy lahars, and probably other areas as well, given the volume of material already on the slopes and more being added every day:

There’s no end in sight with this Sinabung erupsi, and no one knows what will happen next.

I have read that if the current lava dome up there completely collapsed (and the pyroclastic flows are basically partial collapses of this very unstable structure), the resulting huge surge would wipe out everything within 8 km of the volcano. That includes the village where this webcam is situated.

Clearly, it seems, that exclusion zone needs to be extended. But how can they do that? There’s no place to put all the additional people.

Is the eruption connected to nearby Toba? Probably not, but again, nobody really knows for sure.

When will this terrible nickel-and-diming eruption cease? Will it increase? How likely is the scenario, suggested by the Japanese scientists linked above, that part of the mountain might collapse under the weight of the dome, causing a lateral blast a la Soufriere Hills on Montserrat in 1997?

No one knows for sure.


** “Supervolcano” is a controversial term both because it has no scientific meaning and because it’s usually associated with scare headlines in the media for stories that have a tenuous (at best) connection with geological reality. I use it here at the blog because Jacob Lowenstern has defined it informally for “volcanic events in which at least 300 km3 of magma are explosively evacuated from a subsurface magma chamber … and deposited on the countryside as pyroclastic (i.e. fire-fragmental) materials—ash, pumice and rock fragments” – what’s good enough for the Scientist-in-Charge at the Yellowstone Volcano Observatory is plenty good enough for this amateur, too.

Categories: Sunday morning volcano, volcanoes

Tags: , , ,

2 replies


  1. Mount Sinabung – Flight To Wonder

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