Saturday, May 19, 2007

Looking for drowned mammoths

A series of enormous prehistoric floods that killed hundreds of innocent mammoths have been the subject of increased scientific and political attention this spring. The floods, known as the Glacial Lake Missoula, or Bretz, Floods, occurred twelve to sixteen thousand years ago at the end of the last ice age. They were among the largest floods known to geologic history and shaped much of the landscape of Eastern Washington. They were also incredibly cool.

Last week, Coturnix pointed me toward the following news release. It has mammoths, he said, I should comment on it.
Pacific Northwest National Laboratory geologists have put out a call for teeth, tusks, femurs and any and all other parts of extinct mammoths left by massive Ice Age floods in southeastern Washington.

The fossils, in some cases whole skeletons of Mammathus columbi, the Columbian mammoth, were deposited in the hillsides of what are now the Yakima, Columbia and Walla Walla valleys in southeastern Washington, where the elephantine corpses came to rest as water receded from the temporary but repeatedly formed ancient Lake Lewis. PNNL geologists are plotting the deposits to reconstruct the high-water marks of many of the floods, the last of which occurred as recently as 12,000 to 15,000 years ago.

"Now is the perfect time to collect geologic and paleontologic data," said George Last, a senior research scientist at the Department of Energy laboratory in Richland, Wash., whose sideline is researching the ice-age floods. "Winter has eroded the slopes, exposing new evidence. We're interested in researching any known or suspected mammoth find, to collect additional evidence and to improve documentation of those sites."

This is more than a story about mammoths, it actually a story which combines several of my interests. Naturally, the fate of the mammoths is number one, but the Bretz floods are a close second. The Northwest has a fascinating geologic history and the floods are one of the most dramatic. I hope to make a couple of road trips this summer to look at, and blog about, some of the special topics in this story, but today I'll just mention the link between the floods and the mammoths.

The story begins just before the end of the last ice age. Obviously, the climate of North America was radically different at that time. Most of Canada was covered by ice sheets. The eastern and middle parts of Canada were covered by the Laurentian Ice Sheet, which was centered what is now Hudson Bay. In the west was the Cordilleran Ice Sheet, centered on the western mountains. While the Laurentian Ice Sheet crossed the Great Lakes and reached to about the line of the Ohio River, the Cordilleran Ice Sheet barely crossed the Canadian border to cover a sliver of northern Washington, Idaho, and Montana.

The western part of Montana, between the Continental Divide on the crest of the Rockies and the Idaho state line on the crest of the Bitterroot Mountains--an area about the size of West Virginia--is drained by the Clark Fork River. Unlike most rivers in the United States, the Clark Fork flows north. It loops across the Idaho panhandle near the Canadian border and joins the Columbia River in the extreme northeastern corner of Washington. At the end of the last ice age, the Cordilleran Ice Sheet made a sudden lurch southward. A branch of the ice sheet called the Purcell Lobe pushed into Idaho near the location of the present day town of Sandpoint and blocked the Clark Fork. Behind the Purcell Lobe all of the drainage of the Clark Fork was damned up, eventually to form a Great Lake sized body of water called Glacial Lake Missoula. When the lake was full, the future location of the town of Missoula was beneath a thousand feet of water.

Because ice is lighter than water, an ice dam must be about ten percent higher than the water behind it to be stable. When the water that had been gathering behind the Purcell Lobe began to approach the top of the glacier, the situation became unstable. That situation was reached when the water was almost two thousand feet deep at the dam. The pressure at the bottom of the dam was enough for lake water to force its way under the glacier. The water then floated the southern tip of the Purcell Lobe and began to rush out under it. Within a few hours time, the glacial dam collapsed and was torn apart by the rushing water.

A wall of water almost a half mile high blasted out of the mountains into Eastern Washington. These are the floods. I call them the Bretz floods after their discoverer, J Harlan Bretz (the J doesn't stand for anything; Bretz's parents were too poor to afford a first name for him, so he only got a letter). Other writers call them the Glacial Lake Missoula floods after their source. Still others have other names. In any case they are among the largest floods in known geologic history and the most dramatic event in recent Northwest geology.

Most of Eastern Washington is a plateau formed by enormous volcanic basalt flows formed over ten million years ago. The Columbia River flows in a large loop around the northern and western sides of this plateau. During the ice ages a fine dust, churned up by glaciers in the Cascade Mountains had covered this plateau with an deep, rich topsoil. When watered properly, this land is incredibly fertile. Even in the close proximity of the Cordilleran Ice Sheet it would have presented an irresistibly attractive feedlot for grazing and browsing animals. Animals like mammoths and mastodons.

When the waters of Lake Missoula blasted into Eastern Washington, they skipped the loop of the Columbia and traveled across the plateau. The flood tore up entire counties worth of topsoil and carried it away. It deposited enormous gravel bars. It changed the course of rivers. It carved massive canyons in areas that are now desert. It drilled lake-sized holes deep into the basalt bedrock.

In places the flood is believed to have passed as a five hundred foot high wall of muddy water traveling at up to one hundred miles per hour. It pushed hurricane force winds ahead of it. The water itself was a churning brown mass the color and texture of a runny chocolate milkshake. It carried with it topsoil, rocks, trees, entire herds of mammoths, and the icebergs that had formerly been part of the Purcell Lobe. For two weeks, the Columbia carried several times more water than all the rivers in the world combined.

Where the flood ran into narrows, it backed up to form gigantic temporary lakes. These lakes backed up side valleys and there, when the water slowed down, it deposited some of its load of soil and rocks. The topsoil of Eastern Washington has made the valleys of the Yakima, Walla Walla, and Willamette some of the most productive agricultural area in North America, especially for wine. Geologists have named each of these temporary lakes.

The greatest of these stoppages happened at the point where the Columbia River leaves Eastern Washington and turns due West to form the Washington-Oregon state line. At this point, the Columbia passes through a gap in the Horse Heaven Hills. This gap--the Wallua Gap--is about a mile wide and a thousand feet deep. The floodwaters were so vast that they found this gap much too small to pass through. They backed up and overflowed the hills to either side of the gap. Channels carved into the top of the ridge testify to this. The lake that backed up into Eastern Washington is called Lake Lewis. This is the lake that Dr. Last has been studying.

In this map, the light blue shows the furthest extent that the Cordilleran Ice Sheet reached about sixteen thousand years ago. Glacial Lake Missoula is the dark blue area on the left. The Purcell Lobe ice dam is marked by a yellow dot. The dark blue in the center is another ice-dammed lake called Glacial Lake Columbia. The floodwaters from Lake Missoula entered Lake Columbia near the present day site of the city of Spokane and immediately overflowed Lake Columbia's southern banks. The brown area in the center of the map is Lake Lewis formed by floodwaters backing up behind Wallua Gap. The gray area between Lake Columbia and Lake Lewis is the area torn up by the escaping Lake Missoula floodwaters, an area called the channeled scablands. The gray areas below Lake Lewis are the subsequent lakes formed as the flood moved on to the sea. Notice haw far the flood backed up the Willamette River valley into Oregon. (Map source)

Although Lake Lewis only lasted for a few days, it slowed the floodwaters long enough for some of the matter churned up and animals killed to settle out. What's more, the rapid silting buried the dead animals in conditions almost custom made for fossil preservation. It is this bathtub ring of fossils that Last hopes to study.

The Lake Missoula flood wasn't a singular event. After the waters rushed out, the Purcell Lobe pushed forward and blocked the Clark Fork valley again. The river backed up and formed a new lake. After forty or fifty years, it was deep enough to float the glacier again and flood the Columbia again. This cycle dominated the Columbia valley for over two thousand years. There is sedimentary evidence of between forty-one and eighty-nine floods, although at least two came from lakes other than Lake Missoula. Midway through the floods, Mt. St. Hellens was good enough to erupt and lay down a layer of isotope rich and easily dated ash to help geologists understand the sequence of the floods.

Last summer when I added the Bretz floods to my short list of current obsessions I immediately wondered how the floods might have affected the northwest mammoth populations. The first flood would have wiped out almost all of the mammoth population in the plateau and lower reaches of the Columbia River. With subsequent floods coming every forty years or so and mammoths having a very slow period of natural increase, I wondered if the population would ever have recovered. On the other hand, a few years after each flood, those valleys must have been filled with tender young trees and brush, which would have made them terribly attractive to grazers and browsers from surrounding areas, especially in Eastern Oregon, which is a continuation of the same plateau and would have hosted the same wildlife. That growth would have had the effect of luring the mammoths and mastodons back in just in time for the next killing flood, extending the population impact over a much larger area than that of just the flooded valleys. The floods must have had a major influence on wildlife populations all over the Northwest.

George Last tells me that these are exactly the questions he is trying to answer. I'm glad. I think that there is a lot to be learned from reconstructing the geologic and environmental history of the Northwest. Fifteen thousand years ago this region went through a brutal environmental change. The floods were only one part of a major climate shift that accompanied the end of the ice age. Over the next century the Northwest will go through another major change. That process of change began about two centuries ago when Europeans began to settle here, to place new stressed on the plant and animal resources, and to introduce new species into the local environment. Climate change is the latest phase of pressure that we have brought, but it is only part of the story. By understanding how the local environment responded to past changes we might better respond to future ones. Or not. At least by collecting all of the data we can, we'll have a good chance of managing the current one intelligently.

Last and I are not alone in hoping to increase awareness of the Bretz Floods. The Ice Age Floods Institute, with chapters in Washington, Oregon, Idaho, and Montana has been lobbying Congress for years to recognize the flood region as a significant part of the nation's, and the world's, natural heritage. Their main priority has been to get the Park Service to establish a system of official trails to protect key locations and create educational signage along six hundred miles of trails stretching from Montana to the coast. The trail plan only affects land already in the public domain; it does not seize any private land. The plan would cost eight to twelve million to establish the system, which is chickenfeed compared to many government projects. Last is an important member of the institute; I would be a member too, but I'm not joining anything until I get a job.

It's an idea whose time seems to have come. A number of trail guides have appeared in recent years that tell the story of the floods and guide hikers to some of more interesting artifacts of its passage, like giant erratic boulders and mysteriously dry waterfalls in the desert. Nova filmed an episode about the floods back in 1979 and has recently rerun it and released it on DVD. A collapsing ice dam and endangered mammoths were the main plot of the animated movie Ice Age 2.

To establish the trail, both houses of Congress need to pass identical bills creating the system. During the last session of Congress, similar bills were passed in both houses, but Congress adjourned before a compromise bill could be agreed on. This year, identical bills were introduced in both houses--eliminating the need for a conference bill--and the Senate bill made it out of committee, but so far neither bill has made it to the floor for a vote. It has the support of the leading Democrats and Republicans in the Washington delegation as well as members of the Idaho, Oregon, and Montana delegations. The bills are and S 268 and HR 450 both entitled To designate the Ice Age Floods National Geologic Trail, and for other purposes.

This might not sound like the most important use of your activist energies, but, like piecing together the past, it's all part of a bigger picture. In this case, the trails are part of the educational side of the program. If you love mammoths, you'll write to your congresscritters and demand that they push this one through. And, if you happen to be passing through Eastern Washington and notice a dead mammoth by the side of the road, be sure to give Last a call.

Correction - George Last wrote to me point out that I had misidentified his title. He's not a Doctor, but he does have a Master's degree in Environmental Science (Hydrogeology Option). Sadly, there is no title for those of us with "just" Master's degrees. I once pushed for "Magister," a title that is still used in some European academic systems, as the best candidate. But, like most of my language suggestions, this one has not gained much traction.

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