Tunnel Valleys and the Ice Age

A few weeks back, I met up with Rusty Swingset and his lady friend Jacqueline Hyde (who was not quite herself) before they headed back up to the Darwin Ranch near Deception Pass. They were discussing tunnel valleys, something I had never heard of before. Turns out some are a few days' ride (a few hours by car) from me.

Tunnel valleys like Finger Lakes are puzzling to geologists in many ways. They were formed by melted water moving rapidly under glacier sheets.
Finger Lakes image credit: NASA
Just south of Lake Ontario in the state of New York is a region called the Finger Lakes. You can see why (besides, "Clawmark Lakes" could seem a mite scary), since there are about eleven of them going pretty much north and south, and quite narrow. How did they get there?

Tunnel valleys like this are in many places when Earth wore an ice hat. More specifically, areas that were glaciated. Rapid meltwater during the Ice Age carved them out, but the timing details are sketchy. Some uniformitarian geologists think these happened over several ice ages, but they cannot provide evidence. More likely, the flows were catastrophic and at one time more recently than secular geologists believe.
Tunnel valleys are found over numerous glaciated areas, such as the outer continental shelf off Nova Scotia; southern Ontario, Canada; northern Alberta, Canada; east-central Minnesota and Wisconsin, USA; north-west Europe; and the central Barents Sea. . . .

Tunnel valleys have also been discovered offshore. Some of the largest and best documented occur in the North Sea, and are thought to have formed over multiple glaciations, and then infilled by sediment from European rivers.

After a tunnel valley is first cut, it is usually (but not always) filled in. The Finger Lakes of New York are examples of tunnel valleys that were partially filled in with sediments. The sediment fill is varied, and includes glacial till, glaciofluvial sands and gravels, sediment gravity flow deposits, and glaciolacustrine silts and clays.
To dig into the entire article, click on "Tunnel valleys can be formed in one ice age by catastrophic flow".

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