- [Teacher] What does it mean to be curious?

For my students, curiosity creates opportunities for a bigger and brighter future.

(bright gentle music) (light gentle music) (light acoustic music) - This is Pateros, Washington, north of Chelan.

It's a river town where the Methow joins the Columbia River, and this is an incredible place to study the Ice Age.

Thousands upon thousands of granite boulders, laid here low next to the Columbia, across the river, totally different kinds of boulders, dark brown, huge haystack rocks.

And above town, the Great Terrace.

All of these are from the Ice Age, a narrow window of time between 17,000 and 14,000 years ago.

How did this all happen?

(bright upbeat music) (bright acoustic music) (bright acoustic music continues) Well, these are familiar.

These are haystack rocks, glacial erratics, made out of basalt.

There's hundreds of them up here, and there's glacial till carpeting the floor of this area, and underneath some of these glacial boulders.

We know ice was here, therefore, the Canadian ice sheet was right here 17,000 years ago, dropping these stones and the glacial till below.

We know that around the world, we've seen glacial till in ice environments.

But the boulders of Pateros, down low in the valley, are totally different, tell a completely different story, even though those boulders were also being dropped around the same time.

(bright gentle music) (bright gentle music continues) So does that mean that every boulder out here in North Central Washington is 17,000 years old and deposited directly by the ice?

No, these aren't haystack rocks, these aren't basalts.

These don't have glacial till in the floor of them.

These are granites that are sub-rounded and clustered together here in the floor of the Columbia River Valley just south of Pateros, there's a totally different Ice Age story here.

It's an Ice Age flood.

These boulders got tumbled down the valley and placed here, and we know the date.

They came to arrest here during a flood 14,000 years ago, and we know that date because the surface of these boulders have been sampled, and using a technique called surface exposure dating, measured in the lab, we know how many years these boulders have been exposed to radiation.

Where did this flood come from?

How many miles did these boulders get carried?

And there's a completely different land form not far away that also gives us clues about the timing of what happened here in this valley during the Ice Age.

(bright gentle music) (bright gentle music continues) But there's more here than boulders at Pateros.

There's a larger, more extensive land form that's visible here at Pateros, but it extends all the way up to the Canadian border, it's called the Great Terrace, you can see it.

It's a flat with orchards on it.

There's a rise and then a flat, and they match on the opposite side of the Columbia Valley, as well.

You can see that there's multiple terraces, but the Great Terrace is the highest and biggest surface.

Why is the Great Terrace here?

Why does extend so far up the valley into the sides, as well?

There's controversy among geologists.

Let's take a peek inside of the terrace, see if we can make progress.

(bright gentle music) So these terraces from a distance are so simple, but when you look at the insides, the guts of the terrace, it's a different story.

These rocks are all rounded, but the sizes are so different and the stones are so different that this is the core of why this is such a controversy.

How do you explain all of these stones in these terraces on both sides of the valley, at different levels, besides?

It comes down to visualizing what this valley looked like as the ice was leaving the area.

Option one is that the middle of the Columbia Valley had a tongue of ice, as the ice is wasting away, that ice tongue sits in the middle of the valley.

And all of this energy, all of this water energy, building this incredible pile of terrace material is happening simultaneously on both sides of this ice tongue that's in the middle.

And the ice tongue eventually wastes away, we're left with a hole, and we have our matching terraces on both sides.

That's one idea.

The opposite idea is that all these rocks are brought in by running water after the ice has recently left, and we have an open Columbia Valley.

And so therefore, all of these rocks are filled, the entire valley from rim to rim, up to the level of the Great Terrace.

And since that time, the Columbia River scoops a bunch of the material out from the middle.

Those are the two competing ideas.

Regardless of that option, the last event, after we have an open middle, our 14,000-year-old Ice Age flood, the Pateros boulders.

At Pateros, Washington, a chronology of Ice Age drama, all here for us to enjoy.

(bright upbeat music) - [Announcer] This series was made possible in part with the generous support of Pacific Science Center.