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

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.