Eskers

By: Paul Karrow

Eskers Narrow, irregular, steep-sided ridges of sand and gravel are found in many places in Canada. In southern Ontario these ridges, called eskers, are best seen in southeastern Grey County and east of Peterborough. They twist and turn, rise and fall, have gaps, and sometimes have shallow valleys along their trend (known as tunnel valleys). In some areas, eskers are sought out as sources of sand and gravel for road construction and some eskers have been entirely carried away by the truckload. Some have been protected as ANSI's (Areas of Natural Scientific Interest) because of their interesting form.

Eskers mark the former beds of meltwater streams, and they are discontinuous because streams deposit sediments only in certain places along their course. In most cases eskers were formed by meltwater streams flowing in ice-walled tunnels under glaciers. When the glacier melted away, the stream bed was left "high and dry" elevated above the surrounding ground over which the glacier flowed. As meltwater streams and glaciers both tend to flow downhill, both trend in about the same direction, parallel to ice flow and perpendicular to piles of debris forming end moraines along the edge of the ice.

As ice walled the esker-forming meltwaters, sometimes blocks of ice fall into the stream, later to form kettle holes in the esker when the glacier and the ice blocks melted away. Heart Lake is a kettle lake formed in the Brampton esker, west of Toronto.

Eskers can have lengths of tens of kilometers and heights of 5-30 m. The longest in southern Ontario is the Boulter esker, with a length of 160 km and is traceable from Mattawa to Washago near Orillia.