That sinking feeling: Sandy Hill’s geological hurdles

Samuel Close

It’s no secret that Sandy Hill’s terrain can be difficult at times to navigate, as anyone making their way up an icy incline can attest to!

Geography is a crucial part of the identity of our community and has shaped its history and culture in ways that are not immediately obvious.

Sandy Hill’s namesake hills increase in elevation as one travels north and west, with another milder slope to the south. This forms a three-planed depression of sorts facing the Rideau River and Strathcona Park to the east.

The geology of Sandy Hill and the surrounding region is dominated by rock formations from the Precambrian and Paleozoic eras. This allows us to better understand the soils of Sandy Hill.

The topmost strata has three components: (1) a thin strip of gritty sand atop a larger deposit of clay, (2) glacial deposits known as till, and (3) a hard layer of bedrock, deep underground.

Clay found here is often of the troublesome Leda, or “quick” variety, and is prone to rapid dissolution in the presence of excess water, as in a flood or heavy rainfall. This can cause landslides. The glacial till on the other hand was deposited by the ebb and flow of the ancient Champlain Sea some 10 to 12,000 years ago as the vast glaciers that once covered North America in the last ice age retreated.

These geological characteristics have led to a variety of challenges in the development and maintenance of structures in Sandy Hill. This can be seen at street level by the conglomeration of larger apartment and residential complexes in the extreme north and south of the neighburhood, where the landscape plateaus for a short while. Contrast this with the smaller, single-family dwellings more common in the hillier portions. The tendency for older houses to sink through their foundations over time is not uncommon. The weight of their building materials, such as brick and stone (versus lighter wood, for example), only accelerates this process.

Various restoration techniques exist to slow or even reverse the effects of this sinking and subsidence. Unfortunately, many are out of reach to the average citizen due to their high cost and the tendency of insurance companies to classify this increasingly common phenomenon as normal wear and tear rather than something caused by the natural conditions of the region. With some luck, early warning signs of this problem can be identified. These include cracks in ceilings or walls, the presence of water, and in extreme cases noticeable bends or curves in the floor.

If it seems there are few upsides to living on this mound we call home, consider the health benefits that come with the extra exercise! The next time you’re loathing that morning walk up one of our neighbourhood’s hills, think how the ground beneath your feet shapes the ways and places we live.

The effects of unstable soil quality can be seen in the 1993 Lemieux landslide, 50 km east of Ottawa on the South Nation River.
Photo S. Evans, courtesy of Ottawa-Gatineau Heritage