Geology of High Park

About Toronto's High Park / Natural History of Toronto's High Park

by Ken Sharratt

High Park shares a common geological history with the rest of the waterfront areas of the Toronto Region. Canadian Shield bedrock is situated about 400 metres below the surface. Sitting on top of this are a number of layers formed at various times over geological history starting with limestone formed when the area was an ancient sea. Over the past 135,000 years, through a series of glacial advances and retreats, additional levels were laid down. The most recent glaciation, which began its withdrawal down the St. Lawrence River valley about 12,500 years ago, set the stage for the creation of Lake Iroquois, a large lake covering the present Lake Ontario basin. The lake was formed from melt water from the glaciers. Because ice blocked the present St. Lawrence River, the melt water from Lake Iroquois flowed south to the Hudson River in what is now upper New York State.

The shores of the precursors to Lake Ontario. City of Toronto, adapted by Oksana Kulczysky.

Lake Iroquois was much deeper than present day Lake Ontario. High Park would have been under sixty metres of water. During this period, large deposits of sand and other fine material were laid down under water over the present shoreline and High Park. Soil analysis has shown that the soils are sandy loams with a topsoil layer ranging from 0 to 14.5 cm in depth. Yellow to bright orange sands are found below this topsoil. The soils have a low organic and nutrient content.

About 12,200 years ago, the St. Lawrence Valley (where Kingston is today) suddenly opened, and the water from Lake Iroquois quickly drained. The situation was like a tilted bathtub with a drain that became unplugged. Two factors exacerbated the extent of the drainage. First, the land in the St. Lawrence area was depressed by the weight of the glaciers, compared to current levels, making drainage more rapid. Second, the ocean was about 100 metres below current levels, since much sea water was tied up in glaciers. This lower level meant that more water could leave the basin.

The resulting new lake shoreline was about 8 kilometres south of High Park. Rivers and streams that previously drained into Lake Iroquois now immediately began to cut into the soft sandy sediments that were formally lake bottom.

In High Park, water flowing through Spring Creek and Wendigo Creek cut deep steep-sided ravines. Spring Creek entered the current park at what is now Parkside Avenue and Bloor Street, then meandered south. Spring Creek had a number of tributaries that can be clearly seen in today's ravines, such as where the adventure playground and the zoo are located. A number of smaller ravines fed into these and the Creek.

These ravines and streams accounted for 50% of the park area. They contained forest vegetation. (HTO page 287). The land left between the ravines, termed tablelands, was sandy and relatively warm. This land supported more southerly plant types including Black Oak woodlands and open areas or savannahs with a prairie understory. (oak savannahs are considered a provincially rare community type). The valley bottoms and slopes were swampy and cooler and supported more northerly species such as cedar, red oak and other such plants.

As time passed, further geological changes affected High Park. The land at the eastern end of Lake Ontario began to rise after the ice had retreated and the weight of the ice was removed. This rebounding of the land reduced the outflow from the lake and caused lake levels to rise. Over the time, lake levels continued rising and the shoreline moved to its current location. When this happened, the valleys of the streams that had cut into the soft sediments were flooded. The wave action along the present=day beaches and resulting sediment movement eventually blocked the mouth of the Creeks, trapping ponds behind them. This is the origin of Grenadier Pond on Wendigo Creek and the marshy area and Duck Ponds at the lower part of Spring Creek. Grenadier Pond is now the City of Toronto's only remaining lakeshore marsh and occupies most of the western side of the park. (Varga, 1989)

View south from Davenport Road over land once covered by Lake Iroquois. Photo: Marcus Mitanis, Urban Toronto

High Park A to Z - L is for Lake Iroquois

Lake Iroquois – The Sands of Time

by Kathleen Keefe

Ever find yourself walking in sand on a High Park trail and wondering, “Where’s the beach?” Well, thousands of years ago it was right here! The body of water now called “Lake Ontario” has changed names, sizes and forms over the past thousands of years. At one time, it was so large that what is now High Park and most of Toronto was at the bottom of the lake, 50 metres underwater. At other times, the lake was so much smaller that present-day High Park would have been high and dry, far north of the water’s edge.

The Shape-Shifting Great Lakes

For two million years glaciers rode back and forth over our continent sculpting the landforms and waterways. The last of these glacial ice ages began about 100 000 years ago with an ice sheet that grew to cover most of North America. It was massive – in some places three kilometers thick. It bore down and scoured with such force and for so long that it scooped big basins out of the bedrock. These basins became the Great Lakes.

The basin that now holds Lake Ontario has held several earlier versions of the lake. The earliest one dates back 80 000 years and is referred to by geologists as Lake Coleman. When the climate continued to grow even colder, ice blocked the basin’s outlets and the water level rose to a new height. Geologists call this next version Lake Scarborough.

Different lake levels. Source: HTO, Ed Freeman, p.27

About 12 500 years ago, when the glacier was finally melting and retreating northward, the lake’s eventual outlet through the St. Lawrence Valley was still blocked by ice. As rapidly increasing melt-water filled the basin, it rose higher and higher to form the largest version of the lake, Lake Iroquois.

The massive Lake Iroquois was being fed by early Lake Erie, early Lake Huron and several streams which are now tributaries of the Don River. The huge lake lapped at its northern shore along present day Davenport Road. Silt and sand were deposited in the shallow-bottomed waters that covered what is now the High Park area. The huge lake drained to the Atlantic via the lake’s lowest point at the time, over the Niagara Escarpment, then through New York’s Mohawk Valley. A few thousand years later, the glacier had melted and retreated far enough northward to open the outlet to the Atlantic via the St. Lawrence Valley. Because the glacier’s weight had been pressing down on this northeastern edge of the basin for a longer time, it became the new low point and water flowed out of the basin like a bathtub draining. The smaller body of water that remained in the basin was the smallest version of the lake and is known to geologists as Lake Admiralty. The shoreline of this smaller lake now lies underwater on the bottom of Lake Ontario, five kilometres out from today's waterfront. There is actually an underwater bluff showing the former shoreline running from Bluffer’s Park in Scarborough to just west of Hanlan’s Point.

Lake Iroquois Reveals its Bottom

As the lake shrank in size, early ecosystems began to form on the newly exposed land. We know from pollen found in deep bogs that the area was covered by a vast plain of tundra and spruce forest. Animals that moved into the emergent ecosystem included mammoths, mastodons, ancient caribou, giant beavers, musk ox, bison, bears, wolves and a particular kind of deer that was living in the High Park area. And then came the humans! This we know because when the lake was small (Lake Admiralty), humans left very clear footprints in the clay shore that is now underwater on the bottom of Lake Ontario.

The March of Local Human Progress

About 11 000 years ago, some of the very first humans to set foot on this continent crossed the Bering Strait and made their way here. These nomadic people built small settlements and hunted with stone-tipped spears. A family of these Paleoamericans left a record of their presence in our area when they walked together near present-day High Park. Their path is recorded in the mud at the bottom of the lake near Hanlan’s Point. In moccasin-clad feet, they walked along the shore of the smaller lake to what is now downtown Toronto, leaving their footprints in the clay. And there the evidence remained, perfectly preserved for 11 000 years! The footprints were discovered in 1908 by a Toronto Public Works crew laying pipe on the lake bottom near Hanlan’s Point. A city inspector is quoted in the Toronto Evening Telegram, “It looked like a trail. You could follow one man the whole way. Some footprints were on top of the others, partly obliterating them. There were footprints of all sizes, and a single print of a child’s foot.”

Sketch of Footprints from 1908. Source: Toronto Star, November 23, 2008

Unfortunately, you cannot see these 11 000-year-old footprints anymore. Because the city didn’t want to slow down the progress of their tunnel, they went ahead and poured concrete over the prints. Nevertheless, we know for certain, that our High Park was part of an ecosystem with plants, animals and people 11 000 years ago!

On the Rebound

The earth’s surface behaves like memory foam in slow motion, rebounding to its previous level once the heavy weight of the glacier stops squishing it down. About 8 000 years ago, when the basin’s northeastern edge rebounded faster than the other areas, the flow of water into the St. Lawrence slowed down and the lake’s water level began to rise again. Somewhere between 3 000 and 5 000 years ago, the connecting watercourses changed as the lake assumed its current water level and approximate shape. Two tributaries feeding that lake of old were Wendigo Creek and Spring Creek. Sand bars formed across the mouths of the creeks as the rising lake deposited sand and gravel and the surrounding land rebounded. The backed-up water then formed Grenadier Pond and the Lower Duck Pond. The rebound of the earth’s surface is still taking place today at a very slow rate as this land continues to recover from 100 000 years of glacier weight.

Sources

Ed Freeman Formed and Shaped by Water: Toronto’s early landscape Nick Eyles Ravines, lagoons, cliffs and spits: the ups and downs of Lake Ontario in HTO edited by Wayne Reeves and Christine Palassion, Coach House, Toronto 2008.
A Botanical Inventory and Evaluation of the High Park Woodlands, S. Varga, 1989.

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