The world's supervolcanoes: An eruption is a matter of time

After the tsunami disaster there has been further evidence of earthquake activity around Sumatra. Australia's volcanologist Ray Cas, a professor of the Department of Earth Science, Monash University Melbourne, recently spoke to The Jakarta Post's contributor Dewi Anggraeni about volcanoes and earthquakes.

Question: Can you explain the situation with the supervolcanoes or calderas. Are there any indications of an imminent eruption?

Answer: I have been misquoted in the press who had me saying that the next supervolcano eruption would be in Lake Toba, Sumatra. There are around 100 supervolcanoes or calderas around the world. These have not erupted in the historic times, and therefore it is a matter of time before one does erupt.

I drew analogy with the tsunami disaster on Dec. 26, saying that, the tsunami was an event that was going to happen somewhere and sometime, and of course unfortunately it occurred in the region of Indonesia which was highly populated, and had the disastrous effect.

If a supervolcano erupts, the consequences could be two to three times worse, simply because of the enormity of the eruptions that result from the supervolcanos. Supervolcanoes have the capacity to erupt up to 1,000 cubic kilometers of molten lava, distributed around the landscape as ash and rock debris, and can cause enormous devastation up to 200 kilometers away from the erupting volcano.

Are there any supervolcanoes in the region surrounding us?

Indeed the biggest supervolcano in the world is Lake Toba, which last erupted 73,000 years ago, and that eruption actually had a significant effect on global climate. At the time the global climate was deciding whether to return to the ice age or continue the warming process. Volcanologists and climatologists agree that, that eruption was enough to swing it back to the ice age. The release into the atmosphere of huge volumes of fine ash particles and thousands of tons of a gas called sulphadioxide which combined with water droplets in the atmosphere, blocked out the incoming solar radiation.

And if a supervolcano erupts, and that supervolcano is in close proximity to the oceans, the eruptions usually produce very large-volume flows of gas and rock debris, which we call pyroclastic flows. These are capable of flowing in speeds of tens to hundreds of kilometers per hour for distances of up to 200 kilometers from the volcano.

What is the likelihood of the earthquake activity around Sumatra triggering the eruption of the Lake Toba supervolcano?

Some scientists do think that some eruptions of these supervolcanoes can be triggered by large scales of regional earthquakes, of the sort that has been experienced around Sumatra in the last few months.

In other words, there will have to be very large volumes of molten rocks or magma in the below-the-ground surface, below the volcano. And we will normally see evidence of this, if that is the case. We'll see increased rates of gas release from gas fumeroles, and the opening of new gas fumeroles.

At present, there is no evidence that, that condition exists at Lake Toba. But there is no question that in the future some time, the Toba supervolcano could erupt again. However there is no evidence at the moment that it will happen in the foreseeable future.

What are the normal cycles of supervolcanic eruptions?

Supervolcanoes erupt very rarely. Take Lake Toba which last erupted 73,000 years ago. Before then it was 790,000 ago. So some cycles are tens of years, some hundreds of years. In relation to Lake Toba, because the last eruption was 73,000 years ago, we still consider that Lake Toba is a potentially active volcano.

What can be learned from the tsunami disaster?

The lesson to be learned is that had there been adequate monitoring facilities, and warning systems in place, at least the loss of lives would have been very significantly reduced. The same principle applies to understanding and anticipating the eruptions of volcanoes with potential destructions and hazards.

So the message is, if at all possible we should increase the degree to which we monitor volcanoes, and to help us better understand future possible eruptions.

How do you see the recent earthquake in Padang, and subsequent earthquakes nearby in the context of the wider volcanic activity in the region?

To the west, along Sumatra island there is what is called the Java Trench or the Sunda Trench. This represents a location where a large segment of the Indian Ocean lithospheric plate is being recycled. And it is the recycling of the lithospheric plate and the overlaying plate, the Asian plate, that causes the large earthquakes that have been experienced in the region.

However that trench lies offshore in the ocean and to the west of the island. In the meantime, onland in Sumatra there is a faultline called the Sumatra faultline. Lake Toba is located along part of this faultline. But the Sumatra faultline is not just a single faultline. There are a number of subsidiary or splinter faults, which branch off the main faultline. It is possible that the Padang earthquake you mentioned was related to subsidiaries of the Sumatra faultline.

You don't hear alarm bells from the Lake Toba supervolcano?

At this stage not. One immediate potential risk could be if there was a fault in Lake Toba, if there is movement on the floor of the lake, that could generate some tsunamis in the lake.

How do we know if that happens?

Once an earthquake occurs, seismologists can actually calculate where the earthquake occurred. If it is immediately underneath Lake Toba, then it is likely there has been movement of the crust. The question is whether the movement is sideways or there is a vertical component. If there is a vertical component, it will almost certainly trigger tsunamis within the lake.