Ground collapses in Pasvalys district as cause remains unclear

A new ground collapse near a cultivated field in Buiviškiai village, Pasvalys district, measures roughly 17 to 20 meters across and 7 to 8 meters deep. Lithuania’s Geological Survey classifies it as a large subsidence by diameter and of medium depth.

Although it has been described publicly as a record karst sinkhole, there is not enough evidence to confirm either its origin or a connection with natural karst processes. The Geological Survey’s preliminary assessment is that it could be a technogenic suffosion collapse, meaning human activity or underground infrastructure may have helped create it.

A 120-meter-deep groundwater borehole operated beside the collapse and was decommissioned in 2007. Mechanical suffosion occurs when groundwater washes fine particles of clay, silt or sand into another open space. Over time, the ground loses support and the surface can sink or suddenly collapse. Leaking underground pipes, wells and boreholes can create the conditions needed for that process.

Suffosion can look like a karst sinkhole, but the mechanisms differ. Karst processes dissolve soluble rocks such as gypsum or dolomite, forming underground cavities. Geologists say they need archival geological and technical records, electrical tomography and, if possible, an examination of the borehole’s structure before they can confirm or rule out its influence.

The Geological Survey plans to inspect the site during fieldwork in October and November as part of its karst-landscape monitoring. Until more information is available, the collapse is not considered a direct danger to residents or buildings, but people are advised not to approach it because the edges may be unstable.