Scientists keep eye on five raging volcanoes

The Jakarta Post, Bandung/Padang/Surabaya/Yogyakarta

Scientists anxiously watched five volcanoes nationwide on Thursday, as fears over more natural disasters escalated with four mountains rumbling into life over the past three days.

While thousands of refugees spent a third night in tents having fled the slopes of Sumatra's Mount Talang, where hot ash has been raining down since Monday, much attention focused on Mt. Tangkuban Perahu, which is located near densely populated Bandung city and only a few hundred kilometers east of Jakarta.

Next week Bandung will host more than 50 heads of state, including China's president, at the Asian-African Summit.

While activity on the mountain decreased on Thursday compared to a day earlier, biggest crater on the volcano, Domas, spewed hot ash into the air 21 times.

"The earthquake frequency around the crater has dropped to 47 mild earthquakes compared to 100 earthquakes yesterday. But, although the quake intensity has dropped, as a precautionary measure, we are still closing the area near the crater to the public," said Syamsul Rizal, the chief of a volcanology team stationed at an observation post near the mountain.

With 11 mountains in the country on "watch status", volcanologists were paying the closest attention to Mt. Tangkuban Perahu, Mt. Anak Krakatau and Mt. Talang in West Sumatra, Mt. Semeru in East Java and Mt. Merapi in Yogyakarta.

As of Thursday, activities in the five volcanoes had not increased.

Syamsul said the Talang eruption and increased activities of Tangkuban Perahu and Anak Krakatau were triggered by the giant earthquakes in the Nias and Aceh regions recently.

"The tectonic earthquakes can trigger volcanic earthquakes under several conditions, namely that the volcano has an open crater, has its own fluid or gas sources, has shallow magma or if the volcano is unstable. Needless to say, every volcano has its own characteristics," Syamsul said.

This would explain why the earthquakes did not affect other volcanoes located near their epicenters, he said. "It seems that Tangkuban Perahu and Anak Krakatau are more unstable than those that have been inactive for thousands of years," Syamsul said.

Anak Krakatau -- the "child" of the legendary Krakatoa that blew itself apart in 1883 in one of the worst-ever natural disasters -- was put on alert status late on Wednesday amid warnings of poisonous gas emissions.

No one lives on Krakatau but the peak is a popular tourist spot.

While petty traders on the sides of Tangkuban Perahu had been evacuated despite the "watch" status, hundreds of thousands of people living nearby the slopes of the volcano stayed put in their houses, warily watching the smoking giant.

There have been 21 minor eruptions on the mountain since 1986.

In a separate development, a senior government official in West Sumatra reported the Mt. Talang eruption on Tuesday had caused losses to state plantation company PT Kebun Danau Kembar.

"We have to cease production as ashes have covered our tea plantation," said Andre Tanjung, a manager at the company, adding that the eruption cost the company about Rp 720 million a day (US$80,000).

The 11 volcanoes under the watch of volcanologists are among at least 129 active volcanoes in the country that are part of the Pacific "Ring of Fire" -- a series of volcanoes and fault lines encircling the Pacific Ocean and taking in the Americas, Japan, Southeast Asia and New Zealand.