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Exotic landforms

The setting for much of the novel is the tundra of the western Arctic. Throughout the narrative are interspersed references to landforms with fine but rare names, like pingo and esker. So, I thought I'd take a few minutes here to introduce some of the handsomest.

Pingos are giant mounds that look like nothing so much as inactive volcanos. Rather than a bellyful of magma, however, pingos rise on cores of ice. Originating in either a watercourse or the sodden bed of a drained lake, water accumulates in an underground cavity. Annual freeze and thaw cycles, as well as subsurface pressure, cause the water to freeze and expand, bringing up the earth above it, then partially melt and contract, taking on more water to freeze in the next cycle. A typical pingo is said to rise by about 2 cm per year, so the largest ones must have taken many centuries to form.

Eskers are long walls of unsorted rock that wind across the tundra. To understand how they form, one must recall that not so long ago the Arctic was burried under miles-deep ice sheets. As the climate warmed and the ice sheets melted, meltwater streams laden with sand and gravel meandered through tunnels inside them, slowly wearing away their own icy foundations. Once they reached the bottom, they deposited their sediment in long winding piles like a shadow of the stream that bore them.

Maybe my favourite Arctic landforms are raised beaches. Raised beaches are exactly what they sound like - ocean beaches that are well above and back from the shore. When I first arrived in the Arctic I was mystified by reports by locals that the sea there was receding, and had been for as long as they could recall. If ocean levels are rising further south, I thought, shouldn't they be rising up north too? Turns out nope. Once more we must turn to those vanished glaciers and their ongoing influcence to explain what's happening. Miles thick, the bygone ice sheets of the Arctic weighed so heavily on the Earth's crust that it was compressed into the mantle, a bit like how a floating wharf sits lower in the water when you and all your friends stand on it than when you all jump off. Likewise, when the ice sheets melted, the earth's crust began to buoy back up. The scientific term for this is isostatic rebound. It's been happening ever since the last ice sheets melted thousands of years ago, and it is in process yet. So sea levels in the high Arctic are not falling so much as the shores are rising up.

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