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.