5:00

aerial view of Missoula, Montana

We are near Missoula, Montana. The glacial lake once spread through this terrain among the canyons and ravines of the Mission and Saphire Mountains. Above the town itself, Lake Missoula has left its mark on the foothills.

5:25

ancient shorelines

Ancient shorelines -- etched by waves, not by man -- still scar the hillsides over the University of Montana campus. And yet, our high altitude examination yields still better evidence of the floods at a location northwest of Missoula.

5:40

Clark Fork River

Near here, the Clark Fork River, which drains a large part of mountainous western Montana, was blocked by an ice age glacier. The damming of the Clark Fork and the resulting build-up of water behind the dam became Glacial Lake Missoula. When the ice dam broke, a huge body of water rushed out.

6:10

ripple marks

Turbulence of immeasurable power created ripple marks on the bottom of the lake. And from the air they are easy to see. They look much like the ripple marks one sees on an ocean beach. But the ripple marks of Camas Prairie are gigantic. And they are made of coarse gravel -- not beach sand. Some of them are 30 feet high -- and are spaced 250 feet apart. Massive excavating equipment, used to quarry gravel here, are dwarfed by the ripple marks. It is easy to understand how these huge land features were overlooked by scientists in the time before convenient air travel.

Pause tape and ask:

What are we seeing here?

7:00

Dry Falls

This is Dry Falls. This huge twin dry waterfall was full of water when the floods were going. This thing is several times wider than Niagara Falls and twice as high. The whole width of this thing is several miles wide. No river channel could hold the floods once the huge ice dam failed.

7:20

animation of flood moving along routes

Tons of water -- in a hundred-mile long front -- raced down through 3,000 square miles of eastern Washington. The floods hauled away all of the topsoil along their confused and interconnecting routes. In some places the topsoil washed away had been 250 feet deep.

In the underlying lava rock, the floods etched a lace work of water channels, potholes, and waterfall cliffs that remain in place.

Pause tape and ask:

How has water affected this land?

7:55

bed of dried-up river

We're looking at the bed of a colossal river, suddenly dried up. Water suddenly came during the Ice Age and suddenly stopped.

8:10

Frenchman Cataract

Here is another Niagara-like formation of the chewed-up landscape. This is Frenchman Cataract, a waterfall formation, just north of I-90. Actually, Frenchman might not have been much of a waterfall during the height of the floods. The topography so striking to us was completely underwater then. These huge cliffs would disappear in a flood because of so much water. Even the highest elements would be buried by a hundred feet of it. Frenchman Cataract is a thick layer of rock deposited by a series of ancient lava flows. The Missoula Floods first carved away the topsoil and exposed the lava. Then floodwaters hundreds of feet deep subjected the rock to stresses equal to tons and tons of jackhammer force per square foot. Currents perhaps in excess of 60 miles per hour hauled away mountains of gravel produced by the crushing weight of the flood. The currents plucked out lava boulders and tossed them around.

The same erosive process occurred in countless abandoned channels throughout the scablands.

Note the size of the boulders.

9:30

animation of underwater flow of rocks

"If this thing is full of water hundreds of feet deep, you have lots of turbulence. It can physically pick up large boulders off the bottom, and lift them up hundreds of feet of water and carry them over the rim. The faster the water flows, the more the churning, and the bigger the particles it can lift and transport."

9:50

Wilson Creek

At the town of Wilson Creek, for example, the huge water channel is mute evidence to the forces that play in the floods. The low hill that rises from the valley floor is really a big gravel bar covered by ripple marks.

The water slowed slightly here and tons of soil and crushed rock carried by the powerful current settled to the channel floor creating the bar. Downstream is the remains of the obstruction that slowed the current -- a rib of lava sticking into the channel. This battered wedge of bedrock bore the full force of the flood. "Since the whole valley is full of water and flowing very fast, it wants to go straight and that thing is a major obstruction. So once it starts flowing over it, it really wants to remove it ... moving its way through it, chewing its way into it."

Pause tape:
Explain gravel bars.

Time Marks: 0:00-5:00 | 5:00-10:00 | 10:00-15:00 | 15:00-23:20