Glacial Lake Missoula

Western Montana, rising year after year until it became an enormous lake.

That lake is called Glacial Lake Missoula, after the city of Missoula, Montana, which now sits on what used to be its floor.

At its fullest, the lake held something like two thousand one hundred cubic kilometers of water.

That is roughly half the volume of Lake Michigan, all of it stacked up in mountain valleys behind a dam made of ice.

An ice dam is not like a dam of rock.

Ice floats.

Ice is lighter than water, about nine-tenths as dense, and that simple fact sealed the fate of Lake Missoula.

As the lake grew deeper, the water pressing against the base of the ice dam grew stronger.

They did happen throughout human history and geologic time.

I mean, even in the U.S., you have Lake Missoula, you have an ice dam buildup, and it's this massive flood that runs for months and months and months and years and years and years and wipes away everything in front of it just based on the sheer volume of water.

So that's a common tale.

the other side of the Noah's Ark story is the promise that God makes to Noah that he'll never do such a thing again and shines the rainbow as a symbol of his promise and all that.

And I think what happens is it's drying out.

If you look at high water marks, like we saw, say, over by Missoula, they're parallel.

These things are what we would call sub-parallel, because rather than being straight, they're You know, they're curved.

They have undulations in them.

Composed of different kinds of material.

And which one was on top? Now, the Bonneville one was on top, right?

No, the Missoula was on top, and the Bonneville was the real coarse gray stuff, and the Missoula stuff was the finer buff-colored silt.

And you could kind of see two different directions in it as well.

So brief history lesson.

For like tens of thousands of years during kind of the, the, the Ice Age cycle, um, there was a ice dam that, a glacial ice dam that would back up a ton of water in Northwest Montana, and it would form Glacial Lake Missoula, whi- which sort of encompassed most of Northwest Montana.

And then every so often that, that, uh, ice dam would break, and then a monumental amount of water would flood down the Clark Fork basin through Northern Idaho into Washington, and like flood out the whole like Columbia River basin.

And so it made this, it, it's shaped the landscape from Western Montana through Washington.

... um, throughout this whole area.

So we're like birding this area called the Mission Valley, massive 10, almost, nearly 10,000-foot, uh, craggy peaks right behind us.

And then on the kinda grassy slopes on some of the, um, rolling hills around us, you just, it's like all of these vertical striations in the hill, and that's all various high water marks from- Glacial Lake Missoula.

And so that was really fun to, to explain and to, to, like, point it out and talk about, um, the landscape there is shaped by, like, glacial moraines, which is basically the big pile of gravel that the advancing glacier pushes up as it moves.