An immense hole opened up in the ground on Tuesday in a large Russian city near the Ural Mountains. The 100 to 130-foot wide sinkhole looks to have swallowed several homes.

Russian geologists are searching the site for clues as to what caused the accident. The sinkhole formed shortly after a nearby salt mine flooded. That, plus a 1994 earthquake that occurred in the same region, seem to have been caused by powerful underground currents of highly-pressurised gas commonly found around salt mines.

The mine, called Solikamsk-2, churns out more than 2 million tons of potash, a potassium-rich salt used industrially as an agricultural fertiliser, each year, the Daily Mail reports.

The company who owns the mine, Uralkali, has halted production at the site, evacuated the mine, and instructed more than 2,000 workers to stay home.

The same mine had previously collapsed in January 1995, causing gas explosions in surrounding areas the following day, according to the CDC. Sudden, disastrous events like these are not uncommon in salt mines of this type and can happen even if miners take all the proper precautions.

According to Russian news site V-Kurse, several homes are located nearby the sinkhole, but it remains “unknown whether there were homes in the [sinkhole’s] epicentre.”

At least one Russian Twitter-user, however, suggested homes may have been destroyed. In a tweet, Evgeny Andreev writes “Good luck cottagers,” referring to the people living in the residences in the area.

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