Search for Philippines landslide trigger

Landslides, such as the one which has buried an entire community in the central Philippines, are often blamed on logging.

This is because forest cover can play a vital role in maintaining land stability - both by absorbing the rain that can cause it to slip, and by securing soil and other vegetable matter to the bedrock with tree roots. 

"Loss of forest cover does have a serious impact," said Beatrice Richards, head of forest trade and policy at the WWF. 

Logging was blamed for a similar disaster in December 2003, and Philippines President Gloria Arroyo banned logging in December 2004. 

Hugh Speechly, a forestry consultant who lived in the Philippines for 12 years, said that in fact much of the logging in the country had already taken place. 

"The Philippines has gone from a major timber producing country to one where they import timber," he said, adding that in the 1930s, before it began serious logging, the nation had several million hectares of forest cover, compared with only about 600,000 untouched hectares today.

"Certainly in Leyte, a lot of the forest cover has gone," he said. 

"Because of population pressures, people push more into the upland areas to grow food and to do this they clear land." 

In the case of Friday's events in Guinsaugon, Southern Leyte province, it was not clear whether logging was to blame. 

Local officials and eyewitnesses said the surrounding area was well forested, and the governor's office said deforestation was not the causal factor this time, despite having admitted that was the case in a devastating landslide in Leyte in December 2003. 

But Philippines Congressman Roger Mercado, who represents Southern Leyte, has blamed the disaster, to some extent, on mining and logging in the area three decades ago, Reuters news agency reported. 

"If that's what happened, that's a terrible combination... that is a classic landslide scenario," said Dave Petley, professor at the International Landslide Centre, Durham University. 

He said mining could mean cutting away at the bottom of a slope, thereby making it steeper and more prone to landslides. 

He added that even if this happened 30 years ago, its effects could still be being felt. 

Rainfall 

What experts did agree on was the probable impact of heavy rain in the area for up to two weeks before the landslide. 

"All these extreme disasters are multicausal but there's usually some single trigger at the last minute," said Hazel Faulkner, senior research fellow at the Flood Hazard Research Centre at Middlesex University, London.

The area received about 200cm of rain in the last 10 days, officials said. 

Heavy rain storms are frequent in the Philippines, and was also thought to be the trigger for the December 2003 landslide. 

But Mr Speechly said he was surprised by such weather in February. 

He said that severe storms normally ran between June and December. 

Prof Petley agreed. "This sort of rainfall and landslide action in the Philippines at this time of year is quite unusual," he said. 

The Philippines weather bureau has said adverse conditions since November might be linked to La Nina - a natural cyclical meteorological phenomenon which strikes South East Asia in certain years, bringing heavy rainfall.

Prof Petley said the landslide statistics in the region this year suggested 2006 was a La Nina year. 

The month of January in a typical year would normally see 60 landslide deaths worldwide, whereas January this year saw 283 landslide fatalities, many in Asia, he said. 

A mild 2.6 magnitude earthquake which struck the area just before the landslip may also have contributed to it, although it did not appear strong enough to have triggered it on its own, experts said. 

"The area could have really been ready for a landslide because of the amount of rainfall and if there was a minor earthquake, it might have hastened it," Rene Solidum, head of the Philippines government vulcanology office told reporters. 

Another contributory factor could have been coconut trees in the area, which have only shallow roots, the daughter of Governor Rosette Lerias told the BBC. 

Ms Faulkner said she did not know the exact impact of such a crop on the area. 

But she said that it could be argued that a more shallowly rooted tree would not be as effective at counteracting the gravitational pull of the rainfall, and yet would contribute to the weight on a slope.

17/02/2006

Bron : BBC News

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