Knowing the Most Vulnerable Sinkhole Areas in Indonesia, Anywhere?

YOGYAKARTA - The National Research and Innovation Agency (BRIN) explained that sinkholes are relatively common in Indonesia. The most vulnerable sinkhole areas or those that are potentially affected are usually located in areas with karst landscapes or limestone areas.

Some of the most vulnerable areas to sinkholes include Gunung Kidul, Pacitan, and Maros. Geologically, these areas have a fairly thick limestone layer below the surface.

Quoted from the BRIN website, Head of the Geological Disaster Research Center of BRIN Adrin Tohari revealed that the sinkhole natural phenomenon occurs due to the collapse of the limestone layer below the ground surface. This process is formed over a long time and is triggered by rainwater that is acidic because it absorbs carbon dioxide (CO₂) from the air and the ground surface.

"This rainwater seeps into the ground and dissolves soluble rocks, especially limestone, so that it forms cracks and cavities below the surface," Adrin said in his statement.

As time passed, the surface water and groundwater flowing through the crack caused the cavity to grow larger and weaken the supporting layer above it. When heavy rain occurs, the cavity cover layer becomes thinner until at a certain point it is no longer able to hold the load above it.

Adrin explained that in this condition, the roof layer can collapse suddenly and form a hole in the ground surface called a sinkhole.

He also mentioned that one of the biggest challenges in sinkhole mitigation is the difficulty in detecting the early signs of its appearance. This is because the process of forming a cavity takes place slowly and occurs below the surface of the ground so that it is not easily recognizable visually.

However, the existence of limestone cavities can basically be identified through geophysical surveys.

"Methods such as gravity, georadar, and geoelectric can be used to map the distribution, depth, and size of cavities underground. These methods provide an image of the subsurface conditions so that sinkhole potential can be anticipated earlier," explained Adrin.

Regarding the quality of water found in the sinkhole, Adrin explained that the water usually comes from rainwater and groundwater. Therefore, the suitability of water for consumption cannot be concluded directly.

"Water must first undergo chemical analysis, including clarity, color, odor, taste, pH, harmful bacteria such as E. coli, and heavy metals, according to health standards regulated in the Minister of Health Regulation," he explained.

Adrin also revealed that residential areas that are above the limestone layer have a higher risk of experiencing sinkholes.

One of the signs to be aware of is the sudden recession of surface water flow. According to him, if the water flow disappears suddenly, it is likely that water will enter the underground cavity. This condition must be immediately investigated because it has the potential to trigger collapse.

He emphasized the importance of a science-based approach in understanding and anticipating sinkhole phenomena. There are geotechnical engineering methods that can be carried out as an effort to prevent the formation of sinkholes in limestone areas. The method is cement grouting, the process of injecting cement, mortar, or certain chemicals to fill the cavity in the limestone layer below the surface.

The process begins with drilling from the surface to a certain depth where the cavity is located, then the material is injected through a pipe attached inside the drill hole.

Adrin revealed that the injection of grouting material was carried out using a pressurized pump. In order not to damage the rock structure around the cavity, the pressure and injection volume are carefully monitored.

"Then the effectiveness of grouting is checked through permeability tests or other geophysical tests to ensure that the cavity is filled and the stability of the rock layer has increased," he explained.

He also appealed to the public and local governments in vulnerable areas to be more vigilant and utilize geological studies and geophysical surveys as a basis for spatial planning and mitigation of geological disaster risks.

This is a review of the most vulnerable sinkhole areas. Hopefully useful. Visit VOI.id for other interesting information.