Ratdomopurbo, learning the ways of Merapi

Ratdomopurbo, learning the ways of Merapi

By Asip A. Hasani

YOGYAKARTA (JP): "Let Merapi residents' mystical calculations
decide if they will vacate their village or not, because we
scientists cannot determine if and when the volcano will erupt."

This statement was made by volcanologist Antonius
Ratdomopurbo, chief of the Volcanic Technology and Research
Development Station (BPPTK) in Yogyakarta.

Purbo, as he is more commonly known, is one of the key people
responsible for determining the danger level of the rumbling
volcano. Last August, the status was Waspada (caution), before
being raised to Siaga (alert) on Jan. 10, 2001 and then raised
again to the top level Awas (eruption imminent) on Feb. 10.

Merapi's behavior is wildly unpredictable. People living at
the foot of the world's most active volcano have their own
mystical ways to assess the danger level, believing that the
"modern" equipment scientists use are not entirely accurate. So,
volcanologists like Purbo, who has been watching Merapi for 15
years, choose to compromise.

"We are now watching the lava dome on Merapi's peak which may
slide at any time without warning," he said.

The lava dome consists of an estimated 1 million cubic meters
of volcanic material, piling up following a series of recent
explosions.

If the dome collapses, it means disaster. The sliding mass of
lava turns into dreaded burning clouds of lava with a temperature
of up to 600 degrees Celsius, moving at a speed of around 90
kilometers per hour.

"We do hope that the dome will stay put for a long period of
time, or slide by small fractions so that it will not pose any
danger," said Purbo.

The heat clouds were the most dangerous results of Merapi's
explosions throughout the 20th century, when explosions were less
violent than those during the 19th century, particularly in 1872.

The largest eruption in the 20th century occurred in 1930,
leaving more than 1,300 people dead. "Still, heat clouds were the
main killer," Purbo explained.

Merapi's heat clouds are also the most unpredictable
phenomenon of the volcano.

The volcano's Nov. 22, 1994 eruption demonstrated how its 2.5
million cubic-meter lava dome could unexpectedly drop, despite
the volcano's activity status being set at the lowest level.

The heat clouds generated by the collapse of the lava dome
descended upon Turgo village on the southern slope, killing 64
residents.

"It was a gravitational collapse which was more a consequence
of landslide than volcanic phenomenon from what we could detect,"
said Purbo, who was born in Gunung Kidul regency on Feb. 5, 1961.

"Now we realize that studying Mount Merapi is not only a study
of volcanology, but of landslides and earthquakes too," he added.

Purbo obtained his bachelor degree in 1986 from Gadjah Mada
University, Yogyakarta. His thesis concentrated on the
relationship between the Indian Ocean's waves and Mount Merapi's
volcanic activity.

Assisted by a scholarship from the French government, Purbo
continued his Geophysics research at the University of J. Fourier
Grenoble, in France, where he obtained his doctorate. He wrote
two research papers on Merapi during his studies in France, Etude
de Seismes de Type-A du Volcan Merapi (A Seismic Study of the
Type-A Merapi Volcano) and Etude de Seismologique du Volcan
Merapi et Formation du Dome de 1994 (A Seismological Study of the
Merapi Volcano and Formation of the 1994 Lava Dome).

The Jakarta Post's Asip A. Hasani interviewed Purbo recently
at his BPPTK office on Mount Merapi, located on the border
separating the Yogyakarta and Central Java provinces. Following
are excerpts from the interview:

Question: Mount Merapi hasn't generated a large, explosive
eruption for years, so what makes the volcano remain so
dangerous?

Answer: The heat clouds have been the most dangerous. The
possibility of poisonous gases and stones raining down is not
likely to occur. Even during the largest eruption (ever recorded)
in 1872, heat clouds were the biggest danger.

How dangerous would a heat cloud be generated during the
current activity?

It is possible that a massive heat cloud could be generated
from the one million cubic-meter lava dome formed mostly in 2001,
which is currently in a critical position. Part of it slid on
Feb. 10. Massive heat clouds could occur if the entire 2001 lava
dome collapsed at the same time. The disaster could even be more
unthinkable if the 1997 and 1998 lava remaining underneath also
slide at the same time. Together, they constitute some seven
million cubic meters of lava.

What factors could cause the lava dome to collapse?

There are at least four factors: earthquake; heavy rains which
fall on the volcano's summit for an extended period of time; the
drop of new lava from the top; or a fresh supply of volcanic
mudflow from the earth piling up on the lava dome that could push
the mass down.

How could a collapse of the 2001 lava dome threaten Merapi
residents?

Massive heat clouds will form if at least 80 percent of the
one million cubic-meter 2001 lava dome collapses in the direction
of the residential areas.

How could 1994 heat clouds descend on Turgo village and kill
60 residents?

It was part of the unpredictability of Mount Merapi. First,
the 2.5 million cubic meters of volcanic material contained
within the 1994 lava dome collapsed on Nov. 22, 1994 when all
volcanic precursors decreased to the lowest level for several
days. Merapi's volcanic activity was at its peak between April to
March and only declined in August.

Nobody expected that three months later almost 100 percent of
the lava dome would suddenly drop without any detectable trigger.
Our six-member monitoring team was even on the volcano's summit
examining debris from the 1994 volcanic activity when the dome
collapsed, but did not realize it. That is what is called a
"gravitational collapse".

I was in France at the time but wrote a letter to BPPTK's head
to issue a warning.

Second, the heat cloud hit Turgo village by surprise.

There were many unpredictable events during 1994 eruption;
what have you learned from that experience?

We are more careful in predicting any potential disaster.
That's why I study landslides too, not only volcanology. We are
trying to determine signs of landslide or gravitational collapse.
Unfortunately, Mount Merapi is shrouded by a thick haze most of
the time which makes it difficult for us to observe any physical
changes to the volcano's lava domes.

How active is Mount Merapi?

The volcano is never asleep. It discharges hot lava at least
once a day when in its quietest state. The volcano never stops
erupting geologically.

After 15 years observing Merapi, what is the most important
lesson you have learned?

Gravitational collapse of the volcano's lava dome is now one
of the most difficult mysteries to solve. I hope that there is a
trigger to the collapse and that we can soon discover it. If not,
nobody can predict a 1994-style disaster.

What do you think about the Merapi residents' belief that
their elders can have a mystical vision warning when the volcano
will violently erupt?

Their belief is based on experience they have obtained from
generations upon generations. However, I don't believe in
predictions declaring that the next explosion will definitely
happen on a particular day.

They already know safe places to hide on the slope of the
volcano in case of eruption. It's probably true that some of them
have supernatural visions but they should not make them public
because their reliability is highly questionable.