Police station and residential buildings evacuated after giant sinkhole opens in Bangkok, Thailand.

Several residential buildings as well as the Samsen Metropolitan Police Station remain closed after a sinkhole approximately 30 m wide and more than 15 m deep opened up beneath the Samsen Road in the Dusit District of Bangkok, Thailand, on Wednesday 24 September 2024. The nearby  Vachira Hospital has been able to remain open, benefiting from a system of deep piles intended to keep it stable during Earthquakes. The sinkhole swallowed a number of vehicles, as well as several electricity pylons, but nobody was injured during the incident.

A massive sinkhole which opened up in Bangkok, Thailand, on 24 September 2025. Chalinee Thirasupa/Reuters.

Sinkholes are generally caused by water eroding soft limestone or unconsolidated deposits from beneath, causing a hole that works its way upwards and eventually opening spectacularly at the surface. Where there are unconsolidated deposits at the surface they can infill from the sides, apparently swallowing objects at the surface, including people, without trace. 

Bangkok is known to be prone to such problems, being situated on a flat plain of alluvial sediments, and having historically suffered from widespread subsidence due to over-extraction of water from underlying aquifers. This incident was initially linked to heavy rainfall in the area, linked to the local rainy season, which peaks in September. However, subsequent investigations have suggested that vibrations from tunnel excavations for a new subway system may have led to the breakage of a water main, causing water to gush into, and erode, the soft sediments beneath the Samsen Road.

Water gushing from a broken water main into a newly opened sinkhole on 24 September 2025. Thailand Construction News.

Soil liquefied by the initial water main break flowed into the under-creation Purple Line Tunnel, creating a void which undermined further water mains, causing them to sag and break, releasing more water and causing the rate of erosion to increase, leading to the dramatic emergence of the sinkhole at about 7.00 am on 24 September. 

This situation was made worse by initial attempts to fix the problem, which involved pouring 700 cubic meters (about 1500 tonnes) of liquid concrete into the hole. This concrete also found the gap into the tunnel system, with its additional mass causing a 30 m² breach into the tunnel system to open up, through which the concrete flowed into the tunnel.

Engineers must now wait for the concrete to set before clearing out and stabilising the breach, then filling in whole, whilst at the same time preventing water from the seasonal rains entering the hole. Initial concerns that the newly constructed Samsen Metropolitan Police Station would need to be demolished have now been dispelled, but engineers are warning that it may be over a year before it is possible for it to reopen. 

See also...

Surface rebound on the Bangkok Plain.

A number of fast growing cities around the world have suffered subsidence as a result of over-extraction of water from aquifers in recent decades, in some cases resulting in severe damage to buildings and infrastructure. Many cities have attempted to mitigate this, either by regulating groundwater pumping or, in more extreme cases, deliberately pumping water back into affected aquifers. However the relationships between over-extraction, subsidence, decreased pumping and surface recovery are poorly understood, particularly as these are slow processes, where subsidence will generally persist for some time after measures to mitigate it are introduced.

In a paper published in the journal Geochemistry, Geophysics, Geosystems on 14 February 2014, Kazuya Ishitsuka of the Department of Urban Management at Kyoto University, Yo Fukushima of the Disaster Prevention Research Institute, also at Kyoto University, Takeshi Tsuji of the International Institute for Carbon-Neutral Energy Research at Kyushu University, Yasuhiro Yamada and Toshifumi Matsuoka, also of the Department of Urban Management at Kyoto University and Pham Huy Giao of the School of Civil Engineering at the Asian Institute of Technology in Pathuthani, Thailand, describe the results of a study of surface levels on the Bangkok Plain over the period November 2007 to December 2010, using the Phased Array type L-band Synthetic Aperture Radar (PALSAR) instrument on the Japan Aerospace Exploration Agency’s Advanced Land Observing Satellite (ALOS).

Bangkok is situated on an area of flat lowlands close to the Chao Playa River Delta. The city is located on top of a number of aquifers, and previously suffered severe subsidence due to over-extraction from two of these, the Phra Pradang, which is located at a depth of 60-80 m, and the Nakorn Luang, located at a depth of 100-140 m. In 1997 the Thai Government introduced to regulate and reduce the levels of extraction from these aquifers, since when water levels are known to have recovered, though the effect on the ground level is less certain.

A large area (about 250 km²) of the centre of Bangkok was found to be uplifting during the three years of the study. This area ran from the west bank of the Chao Playa River in the west to Suvarnabhumi International Airport in the east, the northern and southern boundaries of the uplift matching roughly the extent of urbanization on the plane. The northwest part of this area uplifted by 2-3 cm during the three years of the study period, the central part by about 3 cm and the southeastern part by about 1 cm. However to the northeast of the area of uplift was an area where subsidence was still occurring; here the ground sank by an average of 1 cm over the study period. This area is home to a large industrial complex.

Areas of ground movement on the Bangkok plain during the three years of the study. (A) Northwestern uplift zone, where the ground rose 2-3 cm; (B) central uplift zone where the ground raised an average of 3 cm; (C) southeastern uplift zone, where the ground rose an average of 1 cm; (D) subsidence zone, where the ground sank an average of 1 cm. Ishitsuka et al. (2014).

As well as detecting ongoing uplift across much of the study area, Ishitsuka et al. were able to detect strong seasonal variations in the amount of uplift occurring. This varied across the study area, but followed a predictable pattern, with the seasonal uplift beginning close to the Chao Playa River, then spreading outwards to other areas. This strongly implies that the aquifers are being filled from runoff from the surrounding plains via the river; however Ishitsuka et al. also consider an alternative scenario may be occurring, where clay particles close to the surface are swelling and shrinking due to seasonal runoff, and note that it is beyond the method used in the current study to differentiate between these alternative scenarios.

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