Shatter Cones: A Bad Day on Earth

Elisabeth Kosters, who at the time was the Managing Director, Canadian Federation of Earth Sciences, points at conical features in a rock exposed close to Laurentian University, Sudbury, Ontario (Photo 1).

Why are those features so significant? They are called shatter cones (Photo 2). They formed about 1,850,000 years ago when an asteroid body or comet collided with the Earth. That asteroid body is estimated to have been 10-15 km (6-9 miles) in diameter. The result was the creation of an impact crater that is estimated to have been up to 250 km (155 mi) in diameter. It is the 3rd largest known impact structure on Earth.

You likely have seen many impact structures during your life. When you look at the moon, those circular craters on the Moon’s surface were created by the impact of an impactor body and the Moon. But, impact craters are harder to see on Earth because later geological processes erased the evidence or substantially modified most of our impact structures. Example, geological processes greatly modified Sudbury impact structure over the last 1.85 billion years. Much of the original structure was eroded away and its present oval shape is the result of a collision(s) between two continents. Despite that geological trauma, the Sudbury structure is obvious on remotely sensed satellite images (Photo 3) and geological maps.

And those conical features? They are called shatter cones. On Earth, they only form in rock that was hit by a meteorite or subject to underground nuclear explosions. They are evidence that the rock was subjected to incredible shock pressure.

The recognition of shatter cones was an important step in understanding the formation of the oval Sudbury basin, its significance as a source of the elements nickel and copper that have been mined underground from the Sudbury area for 140+ years, its influence of the Canadian economy, it influence on labour and health and safety regulations, it influence on environmental changes and societal tolerances to environmental disruption, and the 1971 and 1972 visits to Sudbury (Ontario) of the Apollo 16 and 17 crew members who received geological training on impact structure features similar to what could be found on the Moon.

Clearly Elisabeth Kosters was pointing at an iconic geological feature.

Created: November 11, 2024.