sinkhole also sink-hole or sink hole

a large, circular hole in the ground which suddenly appears because rock below has gradually been damaged or dissolved by water as it passes through the ground

In Britain, the secure feeling of the ground beneath your feet is usually one of life's little certainties. However in recent weeks it seems that even UK residents can't be absolutely sure that they're living on terra firma as they've witnessed a sudden spate of the rare phenomenon of sinkholes.

sinkholes usually appear in areas where underlying bedrock is soluble, so in land masses formed from limestone or chalk

A sinkhole is a large cavity in the ground which abruptly appears because rock below has been eroded by water (it's called sinkhole because it relates to a natural drainage process, providing a route for surface water to disappear, or 'sink', underground). Sinkholes usually appear in areas where underlying bedrock is soluble, so in land masses formed from limestone or chalk, for example. If such land masses have been built upon, the collapse can be so large and deep that it has the potential to literally 'swallow' entire parts of buildings, vehicles etc, with extremely alarming, and possibly very dangerous, consequences.

Sinkholes occur all over the world, perhaps most notably in North America, where they can be hundreds of metres deep and/or wide. However in the UK, they are pretty rare, geologists only typically expecting one or two to appear during the course of a year. In February 2014, by contrast, six sinkholes occurred in different parts of the country within just a couple of weeks. One of the largest was a 35ft wide chasm opening up in a Hertfordshire residential street and causing a number of homes to be evacuated. A 10-mile stretch of a south-east motorway also had to be closed when a sinkhole opened up in the central reservation. This sudden spike in UK sinkholes is thought to relate to winter rainfall, which in 2014 has been the heaviest since records began. The rainfall doesn't actually cause the sinkholes, but it triggers them when large amounts of water need to drain in areas where the rock has been susceptible to erosion. This causes the 'bridges' over pre-existing cavities to finally collapse. Whilst heavy rain doesn't instantly create these underground chasms, it does therefore make them more likely to appear, leading to predictable speculation about the role of climate change and the probability of sinkholes occurring far more frequently in years to come.

Background – sinkhole

The term sinkhole as a description of a geological phenomenon dates back to the late eighteenth century, though the word first occurred a couple of hundred years earlier in reference to a 'sewage pit'. Sinkholes are also sometimes alternatively known as swallow holes, swallets, shake holes or dolines, though the latter usually refers to a shallower, more funnel-shaped cavity (the word comes from the Russian dolina, meaning 'valley').

Sinkhole is one among a number of terms which have been thrown into the spotlight in recent years as a result of significant natural events and commentary connected with climate change. Only in January 2014, we were introduced to the term frost quake as temperatures in Canada hit record lows. In 2012, the word Frankenstorm was all over the headlines when a storm of gigantic proportions battered the east coast of North America, though like the tongue-in-cheek blizzaster, snowpocalypse, and snowmageddon before it, it quickly disappeared off the radar once the main event was over. On a far more serious note, the early part of the 21st century saw the English speaking world become familiar with the Japanese loan word tsunami after the catastrophic Indian Ocean earthquake in 2004.