6 January 2014
Loud explosions heard in parts of Canada are being blamed on a phenomenon called frostquakes. What are they?
Ontario is no stranger to temperatures approaching -20C (-4F) but in recent days the winter freeze has been accompanied by unusual sound effects - bangs waking people up during the night.
@sydney_grieve was one of many to tweet: "Heard a loud bang outside of my room at 2am. My whole family was searching the house thinking someone broke in. #frostquake"
Emergency services in the Greater Toronto Area received reports of loud noises, prowlers and bangs on the roof. Few of those calling in expected to be told it was probably the weather.
Known to experts as cryoseisms, frostquakes happen when moisture that has seeped into the ground freezes very quickly. It expands and builds up pressure, causing the frozen soil or rock near the surface to crack, emitting a sound that people have likened to a sonic boom. (...)
Continue reading: http://www.bbc.co.uk/news/blogs-magazine-monitor-25620598