ICE AGE FLOOD

0:00

city of Portland, light rail, overhead views, animation of waves covering the city

Imagine a city, any modern city. It offers convenience, security, a lot of protection against the unpredictable power of nature.

But sometimes nature is unimaginably forceful. And this is the story of nature out of control. Of a flood that nature unleashed very long ago. Portland, Oregon is a city that has grown in the old flood path. The flood today would swamp Portland's skyscrapers. The buildings would be under 400 feet of water.

Pause tape and ask:

- Does anyone recognize this city?

- How does it look like our city?

- How is it different from our city?

0:50

glaciers calving, sliding down hill

For many thousands of years now, Earth has enjoyed a moderate climate -- one comfortable for human beings.

But just 13,000 years ago, the world was not so friendly. Scientists say some slight variation in the Earth's angle toward the sun made summer weather cooler in the northern hemisphere. The change was enough to tumble the Earth into a deep freeze -- an ice age -- that lasted maybe 15,000 years.

Ask:

- What is happening to the ice?

- Why is it falling?

- Do you know what that is called? (calving)

Pause tape and discuss:

For the last few seconds, what have we been looking at? Rewind the tape and play the scenes of glaciers. Watch and think about what you are seeing.

1:30

animations of the flood

The Ice Age had buried much of the upper half of North America under a very thick sheet of ice.

Near what is now Missoula, Montana, an ancient glacier had blocked mountain rivers and streams, creating an inland sea. By 17,000 years ago, the vast reservoir may have contained 520 cubic miles of water. Its surface covered 3,000 miles.

Pause tape and ask:

Which states are represented on this map?

2:12

animation of lake undercutting, dam failures, Lake Missoula breaking free

The lake was 2,000 feet deep at the point where the ice was holding the water back.

Slowly, pressure forced water under the ice, undercutting the glacier. Finally, in a series of spectacular dam failures, the inland sea -- known to geologists as Glacial Lake Missoula -- broke free.

Pause tape and suggest:

Watch as the ice dam is undercut by water and Lake Missoula breaks free!

2:35

floods across eastern Washington, animation, and then images of the scarred landscape

Lake Missoula probably drained and reformed perhaps a hundred times over 2,000 or 3,000 years. And the resulting inundations were perhaps the greatest floods ever on Earth. Each of the huge roaring torrents bulldozed across much of eastern Washington. They scoured away whole landscapes of eastern Washington's rich soil and pulled up the underlying lava rock. They left behind a scarred landscape that has not healed in more than 10,000 years.

3:15

computer generation of water through the Gorge to the Willamette Valley

And the floodwaters carved a pathway that can still be tracked through the Columbia River Gorge. They deposited much of eastern Washington's topsoil 600 miles away -- in the Willamette Valley south of Portland.

3:25

scientist Richard Waitt, USGS, scraping soil

"A figure that's often used for this is a full bore flood was flowing here at a rate of ten times the discharge of all of the world's rivers. You know that includes things like the Amazon, of course, in that figure. So it's an enormous amount of water. There's nothing like this recorded anywhere else on Earth that we know of." Meet United States Geological Survey Geologist Richard Waitt, "A lot of this stuff is quite rounded. It's traveled some distance ..." Dr. Waitt's careful study of flood sediments reveals details of the floods.

His research -- and that of a pioneer in Missoula Flood study, J Harlen Bretz -- have been essential.

Pause tape and ask:

What is he looking for? (clues in the sediments to the history of the area.)

3:55

J Harlen Bretz

In the 1920's, Bretz's description of the floodwaters -- and his interpretations of the scabbed landscape that they created -- generated scorn among geologists. The floods occurred on a scale so huge, after all, their reality proved almost incomprehensible to Bretz's fellow scientists.

4:35

computer animation of flood over falls

"It's all of Lake Erie plus all of Lake Ontario together. If you can imagine this huge amount of water within two days, maybe, all of it going out and traveling across this landscape. And there's no way the landscape can contain it." Maybe to understand the scale of the floods -- and their impact on the land -- requires aerial study of the path the floods followed. Such a perspective was not available to scientists in the early part of the twentieth century.

Pause tape and ask:

How might having an aerial view of an area help us understand its geology?

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.

10:40

edge of scablands, gentle rolling hills

At the edge of the scablands are gentle rolling hills. The floods made vast tracks of identical acreage disappear. By civilization's standards, the obliteration of a huge percentage of this rolling landscape is a tragic blow to eastern Washington.

"That material is windblown silt that came from the glaciers that were to the north over many glaciations, probably extending back over many hundreds of thousands of years."

Note the difference in landscape appearance.

11:25

harvesting

The rich soil that produces Washington state's abundant wheat harvest is really dust from rocks ground away by huge ice age glaciers. And as we have seen, much of this glacial dust was torn from the region in the Missoula Floods. But along the margins of the flood, some valleys escaped the destructive force of the raging currents.

Pause tape and ask:

How might a valley escape the water? Watch and see ...

11:50

animation, water stalling to form short-lived lakes, slackwater lakes

Sometimes the racing floodwaters stalled temporarily behind bottlenecks in the landscape -- ridges and other land formations. Huge, but short-lived, lakes would grow as the water backed up behind constrictions. The slackwater lakes dwindled away quickly as the floodwaters crashed onward again.

12:15

Walla Walla River Valley left with markers of the flood

But the lakes left behind evidence of their brief existence -- vast layers of sedimentary deposits.

Here is the Walla Walla Valley near the foot of the Blue Mountains. Backwater from numerous Missoula Floods engulfed the valley -- time after time. And each flood left a unique marker here beneath the gently rolling terrain. "Each one of those layers is a record of an individual flood." A ravine in the Walla Walla Valley reveals ancient history in cross section. "The top of each one of those beds was the surface of the valley for probably several decades. Maybe for something between 50 and 30 years, it was sitting here as a dry surface like this until the next flood came in."

Note the depth of the layers compared to the size of the scientists.

Pause tape and ask:

What caused the layers? Watch the video to find the cause.

13:10

scraping the layers to find two thin layers of ash from St. Helens

Sandwiched between two of the slackwater flood deposits are two very thin layers of volcanic ash.

Mount St. Helens is known to have erupted twice in close succession about 15,000 years ago. Each eruption left a dusting of ash in eastern Washington -- now clearly visible between the flood layers. "It's possible to correlate the same deposit from place to place to place all over part of the region. And if you did not have this ash layer, you'd have no clue." Archaeologists think human beings arrived on the continent some centuries after the last of the great Missoula Floods. There were no eyewitnesses, therefore, and presumably no human victims of the floods. But the clues being unearthed point nevertheless to powerful effects from the floods on the modern world. Missoula Flood layers at Walla Walla, for example, correspond to Missoula Flood layers in Oregon's Willamette Valley some 500 miles away.

Pause tape and ask:

Where did the ash come from?

Why is it significant?

Why is it significant that deposits from Walla Walla, Washington match those in Oregon's Willamette Valley?

14:15

Willamette Valley, deposits 100 feet thick from eastern Washington

That means that much of the fertile soil washed from eastern Washington now rests in the Willamette Valley. In the Willamette Valley, Missoula deposits are 100 feet thick in places.

15:00

USGS Jim O'Connor mapping, soil zones

"The soils in eastern Washington that were stripped off and then delivered here have a lot of volcanic materials in it which weather into important nutrients that plants need." Jim O'Connor, like Richard Waitt, is a U.S. Geological Survey geologist. O'Connor's work has produced a so-called "footprint" of Missoula Flood deposits in the Willamette Valley. The roiling Missoula Flood waters got here because the valley is downhill from Missoula. "So in yellow, you see these zones of soils that were very much influenced by the series of Missoula Floods, the glacial floods."

15:20

University of Oregon ongoing study, people at computers, David Hulse

At the University of Oregon, an ongoing study of how human beings use the land confirms the impact of the floods locally. David Hulse heads the U of O's section of Pacific Northwest Ecosystem Research Consortium. The organization includes universities and the Environmental Protection Agency. He describes the flood's influence on how people live in the Willamette Valley.

15:55

computer, how floods affected agricultural uses

"It has conditioned the kinds of agriculture that occurs in those areas. It has conditioned mostly the agricultural uses of those lands." Willamette Valley farmers enjoy rich soil formerly covering the scablands.

16:15

aerial view

That's because tributaries of the Snake and Columbia Rivers channeled the floodwater pretty much directly from eastern Washington to western Oregon. And yet, the flood's legacy is not a simple litany of winners and losers.

16:30

east end of the Columbia Gorge, clues to geography as focus of flood

We know the water got up at least a few hundred feet higher than we are now. To Richard Waitt and Jim O'Connor, it is an ongoing detective story with plenty of hidden drama yet to reveal itself. We are at the east end of the Columbia Gorge. Clues unearthed here point to how the geography of the terrain focused the floods' power as they entered the narrow Gorge.

"This is a site several hundred feet above the river, so you know the water had to get up to this level and go higher. Such a vigorous current was able to transport boulders of this size."

Pause tape and ask:

What clues might prove the flood waters were focused?

17:15

scars on Gorge, computer animation of debris in water "payload"

Scars left by the powerful current mark the high narrow walls of the Gorge to this day. It is evidence that the water got deeper and deeper. As water filled the narrow channel, the depth reached more than a thousand feet. The flow accelerated to 90 miles an hour, gathering an increasing payload of debris. The Gorge contained most of the raging water -- an overwhelming torrent aimed directly at what is now Portland.

17:40

helicopter of Phillipi Canyon leading into the John Day River

But at Phillippi Canyon -- and other locations -- the torrential slurry of dirt and rock and ice overflowed the Gorge. A dry channel is the indelible record of a monumental spillage from the Columbia Gorge at Phillipi into the John Day River. The waterfalls and islands in the channel testify to the violence of what was only a sideshow. Despite its power to drastically alter the land, this secondary spillway did nothing to ease the cataclysmic rush of floodwater.

18:25

west end of the Columbia Gorge, ocean waves

The west end of the Columbia Gorge feeds directly onto the plain now occupied by Portland, Oregon and its suburbs. The sounds of the floodwater -- boulders tumbling and shattering in the torrent -- could have been heard for miles.

18:40

animation of flood filling Willamette Valley, short-lived inland sea

The 400-foot wall of water would have leveled everything in its path. It filled the Portland basin and then raced south to turn the Willamette Valley into a short-lived inland sea.

Such a flood today, of course, would devastate the region. As it is, developers, civic authorities, and the general public must still deal with the aftermath of the flood.

Pause tape and ask students to predict:

What would happen if this flood occured today?

How has the flood affected west and east Portland?

19:10

State Department of Geology and Mineral Industries, Jerry Black, deposits increase earthquake threat because of deposits

"All things being equal we would expect more damage in the areas colored red." A map of earthquake hazards has been prepared here at the State Department of Geology and Mineral Industries. "The reasons it's red here is related to Missoula Flood deposits, absolutely." State Geologist Jerry Black says 50-foot-thick Missoula Flood deposits at Portland's western suburb of Beaverton increase earthquake threat there. The deposits may make the ground unstable in some parts of Beaverton if the ground begins to shake.

20:00

huge boulders in east Portland

And yet, perhaps the greatest flood impact can be found in east Portland. Near the mouth of the gorge, the floodwaters spewed huge boulders and mountains of gravel. Some of the topographical changes brought by the flood are so huge they go unnoticed.

20:10

Rocky Butte, Jerry Black's computer model of Portland

"When you hit, for instance, Rocky Butte, you can see where the water banged into the Butte, formed the bar behind it, wrapped around, and carried out a flood channel." State Geologist Jerry Black has produced a computer model of Portland. The model relies on survey information. All buildings, roads, and vegetation are eliminated. The model shows turbulent currents at the bottom of the flood deposited a huge gravel bar just west of Portland's Rocky Butte.

20:50

Alameda Ridge, ground stable due to size of rocks dropped

"The scale of this is much, much bigger. The scale of the bar runs for several miles -- and Alameda Ridge is the base of that bar." Alameda Ridge -- a comfortable Northeast Portland neighborhood -- is built on a Missoula Flood gravel bar. Of course, the water was about 400 feet deep -- another hundred feet above us here more or less -- and moving, probably, at several feet per second. By the time you get this far down, the flow has dropped most of the big stuff. The current has diminished, but it's still big enough to carry cobbles that are two to three inches in diameter. "The size of the rocks dropped here makes the ground stable. Flood deposits don't magnify earthquake danger on Alameda Ridge."

21:45

"calling cards" of the Missoula Floods, boulder floating on flood

Impact on soil and topography aside, the Missoula Floods left calling cards of their cataclysmic visits to Portland and the Willamette Valley. "It's most likely that this rock came from British Columbia ... "

22:00

animation of icebergs rafting on flood, bringing rocks with them, erratics

" ... probably transported by an iceberg floating in one of the floods." Because the Missoula Floods marked the end of an ice age, huge icebergs might well have been rafted hundreds of miles. Some must have carried a cargo of stone -- stone ripped from mountains as the glaciers carved them up.

22:25

erratics

The largest of such rocks -- called erratics -- known to be in the Willamette Valley is just west of McMinnville. "I suspect that a lot of rocks like this are buried out in the silts of the lowland here. It's just the ones that are up near the upper margins of the flow -- where they were beached up against the hill slopes, up above the lowlands -- that we see."

22:45

scoured land

The floods scoured away thousands of miles of the Earth's surface.

22:55

map of Oregon from space

The scars are clearly visible from outer space and resembled the flood-ravaged landscape of Mars. And yet, Willamette Valley and Portland deposits nothwithstanding, most rock and soil lifted away by the flood has never been found. There's far too much missing. "There's less than a hundredth, probably, of the material that's been removed from this system that we can account for in the gravel bars."

Pause tape and ask students to predict:

Where do you think the missing rock and soil from the floods is today?

23:20

beach waves, helicopter of the Gorge, glaciers calving, sunset

Somewhere under the Pacific, then, lies a mountain of rubble that was the Earth's skin. It washed here as the Columbia River ran at 2,000 times its average flow.

No glaciers are forming ice dams that threaten to turn parts of the Western U.S. into an inland sea. But that is scarcely the final word. The collective memory of human civilization is short, but time is long. And scientists believe there will be another ice age.

Pause tape and ask students to predict:

Could the floods happen again?

What conditions would need to be present for a similar flood?

Do you think humans would be able to prevent or lessen the effects of these floods? Why or why not?