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

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

(upbeat music) (bright tone) (calm music) - There's a big city over there.

It's called Seattle, and that's Elliott Bay in the foreground, a deep body of water with saltwater, marine biology, ferries going back and forth.

This body of water is connected to the Pacific Ocean and the world beyond.

But are you aware that 16,000 years ago, Elliott Bay was not made of saltwater.

It was made of freshwater.

It was a freshwater lake completely cut off from the Pacific Ocean.

How's that possible?

(bright music) (upbeat music) This is Green Lake.

Beautiful neighborhood on a quiet morning just north of Downtown Seattle.

There are clues to the Ice Age everywhere.

16,000 years ago, we had a thick ice sheet from Canada that was right here at Seattle.

And when that ice sheet retreated, a big block of the ice sheet remained.

A giant ice cube was sitting right where Green Lake is today.

The ice block melted, and we have a freshwater lake.

That's one story You can tell ties specifically to the ice sheet, but there's lots of other clues of various forms and shapes and sizes.

In the Seattle area, let's go find some more.

(upbeat music) Green Lake over my shoulder, that's where we just were.

And now, climbing a flank of Phinney Ridge.

It's steep.

In this neighborhood, walking east and west is steep up and down, going up both sides of things called drumlins.

Phinney Ridge is a glacial drumlin.

It's not just Phinney Ridge.

It's Queen Anne Hill.

It's Beacon Hill.

Many of the hills of Seattle are these things called drumlins.

Everything's north-south oriented here.

Have you noticed that before in Seattle?

East, west, up and down, north, south, easygoing the valleys and the ridge tops.

The drumlins are made of sand and gravel deposited by the ice itself.

It's Canadian rocks brought down here and streamed down in a line.

But it's the troughs.

Green Lake sits in one of the troughs.

Elliott Bay sits in another trough.

It's the troughs that are fascinating because while the thick Canadian ice sheet was here, highly pressurized water like a fire hose is digging, digging into the glacial till and making these incredible valleys.

Green Lake, freshwater, Phinney Ridge, drumlin, Elliott Bay saltwater.

Where next on our tour of Ice Age features in the Seattle neighborhood?

(upbeat music) So even Downtown Seattle, is there still an Ice Age story?

There is.

There's that north south Phinney Ridge, Green Lake north south trending ridge and valley story.

That goes underneath the asphalt for sure.

But the real reason we're here in downtown is to look at Columbia Center, the tallest skyscraper in the city.

It's more than 900 feet high.

And to visualize the total thickness of the Canadian ice sheet that crossed the border and got to Seattle more than 15,000 years ago, what's your guess?

Three Columbia Centers tall.

The ice sheet was almost 3,000 feet thick.

That's the elevation today of Snoqualmie Pass.

That's a hell of a lot of ice with weight, power, water, and the profound effect on this landscape is still recognizable today.

(upbeat music) Yet another neighborhood in Seattle, this time the Wedgwood neighborhood.

And another clue from the Ice Age, a giant boulder.

An erratic, a glacial erratic, the Wedgwood erratic.

How did it get here?

Erratics are boulders that do not match the local bedrock.

And this guy and the hundreds of other glacial erratics in the Seattle area better match the bedrock of Canada than they do Washington.

So the bedrock was lifted by the ice, carried as a boulder across the border, and those boulders were dropped here in the Puget Lowland.

Yet another piece of evidence to prove that the Canadian ice sheet was here in Seattle.

(upbeat music) This is Lake Washington, freshwater.

It's a big lake.

Elliott Bay on the other side of downtown, saltwater today, but used to be freshwater.

So what is the story and how does it tie to the Canadian ice sheet?

Here we go.

When the ice sheet advanced over Seattle, 3,000 feet of ice, that ice blocked the Strait of Juan de Fuca between the Olympic Peninsula and Vancouver Island.

That's saltwater of the Pacific Ocean that wants to get into Puget Lowland, but cannot because there's too much ice in the strait.

That's when Elliott Bay was a freshwater lake, and the weight of the ice pushed the land down.

So meltwater coming off of the ice, freshwater and rivers, freshwater rivers from the mountains to the south, they're all ponding on the southern edge of the giant Canadian ice sheet.

Last part of the story, start melting the ice sheet back to the north.

Eventually, we open the Strait of Juan de Fuca and allow the salty Pacific Ocean water to come back into Elliott Bay.

The only two major lakes in Puget Lowland that are still freshwater and were not converted to marine water Lake Washington and Lake Sammamish, along with neighborhood lakes like Green Lake.

The Canadian ice sheet, leaving a lasting impression on the landscape of greater Seattle Washington.

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