Largest Glacial Erratic
Big Rock
Canada ()
A glacial erratic is a large boulder of a rock type different to the rocks of the area in which it sits. Such boulders were transported from their place of origin by glaciers in the last ice age, which picked them up and carried them along as the glaciers advanced, before depositing them on the ground upon melting. The largest erratic boulder identified to date is 'Big Rock', near Okotoks, Alberta, Canada. Measuring around 41 x 18 x 9 m (134 x 59 x 29 ft) and weighing an estimated 16,500 tonnes (36.3 million lb), this block of quartzite was transported around 480 km (300 miles) from the Athabasca Valley, near Jasper, Alberta, between 18,000 and 10,000 years ago.