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Email:
rwp@rockwalkpark.com
Local Geology
The Temiskaming area features a geological diversity that is among the best in the world. The amount of rock exposure, the wide variety of ages, the landscape effects, and the economic spin-offs make this area an outstanding natural geological laboratory.
Lake Timiskaming Rift Valley
This feature that gives us part of our landscape, preserves rocks that are similar to those at Niagara Falls, provides channel-ways to geological features that could enhance our economy, and makes this area one of the few in the Precambrian shield that are subject to earthquakes – The Lake Timiskaming Rift Valley.
Formation of a rift valley
Rift valleys are found around the world. Some of the most famous ones include the East Africa Rift Valley (representing an early stage in plate spreading), and the Rhine Valley or Graben. Essentially, whenever the earth’s crust is subjected to compression or tension, cracks or faults develop, and some blocks of rock drop along these fractures relative to the ground on either side. One can visualize this with a layer of modelling clay on the surface of a balloon. If you add more air to the balloon and increase its radius, the clay will crack, and adjust, with some chunks falling with respect to neighbouring chunks.
The blocks of rock that drop form a valley or depression in the ground surface, which is usually called a graben. The higher ground between grabens is called a horst. Another term for graben and one that emphasizes the origin of these features is rift valley.
The faults that form the boundaries of these valleys and hills are normal faults that in many cases extend very deep into the crustal layer. Because of these deep-seated fractures, two phenomena can occur:
- When the earth’s crust is being subjected to huge forces at spreading and colliding plate boundaries, there have to be adjustments throughout the crust … and these adjustments are easiest to make where deep fractures already occur. Consequently, when pressure builds up, these fractures can move, and earthquakes occur. Although not in the league of, say the San Andreas Fault. Earthquakes in the order of 3 to 5 on the Richter Scale have been felt along the Lake Timiskaming Rift Valley, with the most recent at the start of January, 2000.
- Deep-seated fractures provide channel-ways or openings along which magma from deep within the crust or even the upper parts of the mantle can find its way to positions near surface or even right to surface. One such type of occurrence is an intrusion called kimberlite, which just happens to be the principal host rock for diamond deposits. The Temiskaming region has seen the discovery of numerous kimberlite pipes over the past 15 to 20 years, and although none have yet been shown to be economic, the search continues.
The diagrams below give a general overview of how the Lake Timiskaming Rift Valley developed:
This particular view is oriented as if the viewer was located in Quebec, looking northwesterly to westerly.
The second picture shows the north end of Lake Timiskaming in its geological setting. Two features are worthy of additional mention:
- At the north end of the lake is a promontory exposed to divide the north end of the lake in two. This promontory (actually a peninsula, as it’s joined to the rest of the area just north of the picture) is called Dawson Point. Note the occurrence of Silurian and Ordovician limestones there. In fact, because these carbonate rocks occur in the centre of the rift valley, they have been preserved from subsequent removal by glaciation. The limestone layers, and indeed much of the Huronian layers shown on the flanks of the valley are mostly gone. Erosion by ice, water, and wind has removed almost all, except for two isolated patches (called outliers) near New Liskeard and Haileybury.
The Silurian layers at Dawson Point, in particular, include some more resistant dolostone that’s equivalent to the cap rock at Niagara Falls. Even here, it proves more resistant to erosion, and a cliff results along the Dawson Point peninsula.- The faults responsible for the rift valley are over-simplified in the diagram above. However, the principal one shown on the western side of the valley is called the Lake Timiskaming Fault. In some places, it forms spectacular fault cliffs, such as Devil’s Rock, just south of Haileybury:
