Thursday, August 26, 2004 Experts to probe 'sinkhole' in Sarangani town
GENERAL SANTOS CITY -- A senior official of the Mines and Geosciences Bureau (MGB) said Wednesday a team of geologists would be probing the sinking of a large landmass in Glan, Sarangani next week.
MGB 12 Director Jose Madrona ruled out any possibility of the occurrence being volcanic in nature.
He said the team of experts would be coming from various MGB regional offices and would be assisting local experts in assessing the situation in Glan, some 57 kilometers southeast.
The team would also brief residents and officials on the situation in Sitio Pagang and the geological formation of Glan.
Madrona explained that the sinking of some four hectares of coconut farm in Sitio Pagang, Barangay Baliton, could be attributed to the weeklong rain that hit the area, which was previously identified as landslide-prone.
He said the Pagang sinking is the second incident in the province.
The first was in Malungon town last year, he added.
"It is not volcanic in nature," he said in reaction to persisting reports that the earth movement in Glan was triggered by volcanic activity.
Madrona said the sinking land mass is curvilinear in form "and if the rains would continue, maybe the whole mass will go to the sea."
Residents of Sitio Pagang, mostly ethnic B'laan, frantically fled to safer areas when the ground started to sink last week.
On Monday, the ground already sunk by about nine meters and cracks, measuring two meter wide, continue to widen.
As the ground sunk, the shoreline also rose by about eight feet.
Madrona said they saw scars of the June 18 landslide which could have started the sinking of the ground, which he described as consisting mainly of loose and deeply-weathered rocks and sandstones which could be heavily saturated by intermittent rains.
Earlier reports said the earth movement could be volcanic in nature citing testimonies of residents who claimed to have heard explosions and saw fissures that let out sulfuric aroma.
Madrona said the explosions could have come from colliding rocks and boulder formations, which usually cause a deep-seated booming sound.
Asked if the situation in Glan is similar to "sinkholes" which are common in Florida in the United States, Madrona said they will have to find that out next week when he and other geology experts visit the town.
A website on geology described sinkholes as "a common naturally occurring geologic phenomenon and one of the predominant land forms in Florida."
Sinkholes can be classified as geologic hazards sometimes causing extensive damage to structures and roads resulting in costly repairs.
Sinkholes can be shallow or deep, small or large, but all are a result of the dissolving of the underlying limestone.
Hydrologic conditions, including lack of rainfall, lowered water levels, or, conversely, excessive rainfall in a short period of time, can all contribute to sinkhole development.
The website of the United States Geological Survey (USGS) said sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds, or rocks that can naturally be dissolved by ground water circulating through them.
As the rock dissolves, spaces and caverns develop underground. Sinkholes are dramatic because the land usually stays intact for a while until the underground spaces just get too big.
If there is not enough support for the land above the spaces then a sudden collapse of the land surface can occur.
The collapses can be small or they can be huge and can occur where a house or road is on top.
The University of Florida Soils and Water Science Department website said sinkholes are closed depressions in the land surface formed by dissolution of near-surface rocks or by the collapse of the roofs of underground channels and caverns.
Sinkholes are a natural, common geologic feature in places underlain by soluble rocks such as the limestone and dolomite.
Under natural conditions, sinkholes form slowly and expand gradually.
However, activities such as dredging, constructing reservoirs, diverting surface water, and pumping groundwater can accelerate the rate of sinkhole expansions, resulting in the abrupt formation of collapse-type sinkholes, some of which are spectacular, the UF-SWSD website said. (PNA)
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