I was reading the news from back in Canada today, and came across this article on a massive sinkhole that formed on a road about 180 km northwest from where I grew up in the province of Manitoba. The sinkhole is over 200 m wide, and 5 m deep! That region has been inundated with large amounts of rainfall during the past few years (including a massive flood event last year), but it was the 30 cm in the past month that caused the land to finally say “NO MORE!”
Coincidentally, I have actually been researching the surficial geology of western Canada during the past couple of weeks, so I can actually comment a bit on what has happened here. Over 10,000 years ago, this region was covered by a vast ice sheet. As the ice melted, it left an unsorted sediment known as till. This sediment can be highly variable in composition, and considering the region where this sinkhole occured is topographically variable, it is possible for to could flow or or pool into a concentrated area, such as where this road was. According to the local officials, this section of the road was already known to be problematic, and it just finally gave way.
On a side note, it is summer back at home, I have to say I am a bit jealous after waking up in the frost this morning in Canberra!