May 07, 2014

Ice squeeze carved Erin’s unique terrain

As published in The Erin Advocate

What started out with wondering how Erin village got its big hill has ended up as a story of ice lobes converging, melting and carving out our fascinating landscape.

Geologists say we are currently in an interglacial period – a break between ice ages that has allowed human civilization to flourish. In what they consider a recent event, the Wisconsin glaciation extended into what is now the northern USA. It lasted over 75,000 years and vacated Erin for the last time about 12,000 years ago.

Ice sheets up to 4 kilometres thick came through this area several times, but they did not simply come from the north. The ice built up as huge lobes in the Great Lakes basins and moved outwards.

In a late phase of the last ice age, the Lake Ontario Ice Lobe flowed northwest, up the Niagara Escarpment. It covered the current Erin village and stopped just north of Hillsburgh. Meanwhile, the Georgian Bay Ice Lobe flowed southeast, into the northern part of the current Town.

Between these frontal positions lie the Hillsburgh Sand Hills, part of the Orangeville Moraine, which is a mixture of boulders, silt, clay, sand and gravel, transported from other areas by the ice. Surface drainage is irregular, creating vast swampy cedar wetlands where rain recharges the groundwater.

Sitting at a high elevation in Ontario, this is known as the Headwaters region, with water flowing north to Georgian Bay via the Nottawasaga River, west to Lake Huron via the Saugeen River system (starting in the Dundalk-Mount Forest area), southwest to Lake Erie via the Grand River system and to Lake Ontario via the Humber and Credit Rivers.

A massive amount of rock and soil (known as till) was also being moved under the ice, and rearranged by meltwater. One result is the Guelph Drumlin Field, a series of more than 300 long rounded hills oriented in the direction of the ice flow.

The Erin village hill with the water tower is one of them, a mix of boulders, stones, sand and silt known as Port Stanley Till. It is common in Erin and Caledon (and it is not actually from Port Stanley).

Part of the Hillsburgh Meltwater Channel (Hillsburgh to Alton) eventually became Shaw’s Creek flowing east to join the main Credit flowing out of Orangeville, while another part became the West Credit River flowing south, eventually coming together at the Forks of the Credit. Just beyond Hillsburgh, the meltwater flowed west into what are now the Speed and Eramosa Rivers in the Grand watershed.

The rivers generally follow deep bedrock valleys, but are affected by various meltwater channels near the surface. In the southwest section of Erin’s territory, south of 10 Sideroad, there are hummocky ridges of dolostone rock where the ice sheets scraped away much of the soil.

Sections of the Galt-Paris Moraine are also in that area, dividing the drainage, with the West Credit flowing east towards Belfountain and Inglewood, while the Black Creek / Silver Creek meltwater channel ran south to Georgetown.

The easiest material for meltwater to transport is sand and gravel. When the raging waters slowed down, the network of meltwater channels often filled up with this outwash material, creating huge aggregate deposits close to waterways in the Hillsburgh-Erin-Caledon area.

The meltwater also created temporary lakes, and flood plains that allowed the soil to settle in layers. This created good farmland in some areas, such as the till plains west of Guelph where the ice scraped up large quantities of carbonates, sand and clay from the Salina bedrock formation, then distributed them to form a rich loam.

Information for this article has come from geology and aggregate mining reports by the Ontario Ministry of Natural Resources, and documents from Credit Valley Conservation and the Grand River Conservation Authority. I’d also like to thank John Slack of Erin for his description of the local geology. He is the CEO of Boreal Agrominerals Inc. in Brampton, which produces a natural fertilizer called Spanish River Carbonatite.