The collapse of Turtle Mountain occurred at 4:10 AM on April 29, 1903. It is estimated that 82 million tonnes of mostly limestone fell away from the side of the mountain. The volume of rock was approximately 150 m deep by 425 m high and 1 km wide. When it came to rest in the valley bottom it covered an area of 3 square km. It is estimated that 70 people were killed due to the rockslide.
It is thought that the effects of the underground coal mining may have weakened the mountain and was a primary factor in its eventual collapse.
Debris slides like this one and many others around the world have shown the ability of large rock slides to travel long distances away from their source. It is speculated by geologists that when large masses of rock and debris start moving that they may flow almost like water due to a bottom layer of air or water that lubricates the surface upon which the rock travels. This slide spread over 3 square km in less than 2 minutes. Also buried was the railway which ran along the valley.
An interesting footnote that saved many lives during this event were the actions of a brakeman for the Canadian Pacific Railway. Working on another train in the area at the time, he was fortunate enough to be out of the way of the slide and realizing that a passenger train was due to arrive shortly, he raced across the rocks and down the tracks to flag down an approaching passenger train. He was able to signal the train in time for it to stop before colliding with the slide. Also, 17 coal miners were able to dig their way out of the underground mine after 14 hours of digging after the mountains collapse.
Note: large landslides like this one may be due to a variety of causes. In this case it was likely due to the underground mining weakening the mountain but other causes include, water saturation of the ground (rainfall, snowmelt, etc.), earthquakes, removal of vegetation from the surface (forest fires, logging, etc.), removal of material from below (stream undercutting, road construction, mining, etc.), volcanic events and steep slopes.
While large landslides like the Frank Slide occur infrequently, smaller landslides happen on a daily basis throughout the world and often show up on the evening news when roads and houses are buried.
As of November 21, 2006 to log this Earthcache:
You must e-mail me some unique bit of information regarding the site that you learnt while there. For example you could submit the average size of the rocks from the slide or how deep it is. Posting a photo is not required but appreciated. I will monitor logs and check my e-mails for appropriate information. Unfortunately, any log that does not meet the requirements will be deleted. Thanks for visiting an Earthcache!