Exploring the sands of time

Jessica Waters / Leader Editor

Jagged rivers of icy water sluice across a surreal, ruggedly beautiful landscape, cutting gullies into the glacial surface of the Cordilleran ice sheet.

Jagged rivers of icy water sluice across a surreal, ruggedly beautiful landscape, cutting gullies into the glacial surface of the Cordilleran Ice Sheet.

Spilling onto the barren flanks of the bordering slopes and splashing into the turquoise depths of glacial Lake Missoula, the waters deposit their telltale treasures - from fine-grained silt to tumbling boulders carried from hundreds of miles to the north.

Hundreds of feet below the torrents of the sediment-laden rivers, the southern edge of the advancing glacier bulldozes the native landscape before it in a crescent-shaped ridge.

The leaden pressure from tons of ice scrape and iron the land, sending water from the saturated soil tunneling through ice and earth to escape the tremendous weight in jetted plumes geysering over the frothing waves before splashing back down into the icy lake.

Last Saturday, 17,000 years later, more than 100 people standing on the gently-sloping ridge bordering the southern edge of Polson could almost feel the chill of that arctic scene as geology professor Marc Hendrix, of the University of Montana, described the geological history of Flathead Lake and the surrounding region.

With a vantage point provided by the very ridge of land shoveled before the ancient mass of glacial ice, participants in the Ice Age Floods Institute 2008 fall field trip had a perfect view of the landscape scoured out, cut into, formed and deformed by the Flathead Lobe of the Cordilleran Ice Sheet, the birth and death of glacial Lake Missoula and the resulting formation and stages of ancestral Flathead Lake.

"Flathead Valley is separated from the Mission Valley to the south by the feature we are standing on now - a low ridgeline called the Polson moraine," said Hendrix. "Looking at the sediment at the top of Polson moraine, we are looking at well-sorted sand full of ripples deposited underwater - very clearly indicating a flow to the south and our interpretation of this is that the Polson moraine is largely a sub-aqueous feature; a moraine that was forming at the base of the Flathead Lobe of the Canadian (Cordilleran) Ice Sheet - terminating within the waters of glacial Lake Missoula right about where we stand."

"At full pool, glacial Lake Missoula's surface was about 4,200 feet in elevation, and the crest of the (Polson) moraine is at about 3,000 feet, meaning that there was about 1,000 feet of water above our heads," he added, saying the ice surface of the glacier probably rose a few hundred feet above the surface of the lake, whose full-pool elevation is evidenced in the wave-cut benches eroded into the surrounding hillsides.

Working to provide education and awareness of ice age floods in the Pacific Northwest as vital components of regional, national and international natural history, the non-profit Ice Age Floods Institute sponsors field trips and lectures; acts as a liaison between individuals, organizations and governmental agencies to promote recognition of these ancient floods as significant contributors to both the geology and culture; and spearheads an ongoing effort lobbying Congress for the creation of an Ice Age Floods National Geologic Trail.

Seminars, programs and field trips such as the Flathead Lake tour not only serve educational purposes, but provide intriguiing and enjoyable oppurtunities for members, said IAFI Glacial Lake Missoula Chapter president Norman Smyers.

Progressing along the eastern edge of Flathead Lake, skirting the foothills of the Mission and Swan ranges, the IAFI tour brought to light the geological evidence underpinning the historical tale of the land which Lake County residents call home.

After pulling away from the newly-completed lookout at the crest of the Polson moraine (along the northbound lane of Route 93) the two filled-to-capacity tour buses wound their way along the slow curves of Route 35 and eased off the road at the edge of a rough-faced outcropping of jumbled sediments ranging from small, smooth gravel to basketball-sized chunks of stone - commonly recognized as the deposits of direct glacial contact, according to Hendrix.

"Whatever deposited these sediments didn't have the capacity to sort it very well, as you would expect a river or wind to do," explained Hendrix. "Typically, sediments deposited by rivers or air flows are well sorted, but ice contact tills (sediments) are typically a lot less well sorted. When the ice retreats, it just sort of dumps all of its sediment and leaves it behind as a poorly-sorted sediment."

Crunching along a bumpy drive to the third stop - a working gravel pit where ongoing operations cut deep into the terrain - the self-proclaimed "flood nuts" had a chance to observe the exposed, steeply-sloping layers of a Gilbert-style delta. Formed by rock-bearing flows - like the rivers streaming over and through the frozen mass of the ice sheet - spilling well-washed, water-tumbled and smooth stone into the standing waters of glacial Lake Missoula, the deltas of easily-mined open-framework deposits of gravel provide economic oportunity even today, said graduate student Paul Skudder.

"We know here that the water must have been flowing from the east, and water flows downhill. If you think about that, there is no hill to the west of us, there is just empty space over a lake and this indicates to us that there must have been water flowing off the surface of the Flathead Lobe of the Canadian ice sheet,"said Skudder.

"The glacier would have been receding to the north and water would have been melting and flowing off of it, carrying sediment that was trapped in the glacial ice and that water would have been sorting out the fine grain clays from the rest of the material and the result is that these gravels are extremely clean, with no sand or clay between those pieces of gravel, causing an open framework gravel with a very high amount of open space between the rocks and that is really nice for the people mining this because it is really easy to dig out and very valuable becasue you don't have to process it very much," he added, pointing out that more money is made each year in the U.S. from gravel and sand mining than gold mining.

Moving on through numerous stops as the tour rounded the northern end of the valley and skirted the high-desert hills of the western shore, Hendrix explained various geologic structures and landscape features relating to the Pleistocene period history of the Flathead Lake region - including the cataclysmic draining of glacial Lake Missoula after the failure of an ice dam on the Clark Fork River in Idaho.

Stops at a sand mine and the deep cut of a railroad bed provided the opportunity to observe different classes of sediment layers associated with wind-blown sand dunes and the ecology of Flathead Lake as it shrunk from its ancestral form to its current topography.

A westward turn onto Route 28 took the tour along the path of an arm of the Flathead Lobe which curled off from the main ice sheet blanketing the valley, rumbling up a cut in the sloping foothills - pushing an arc-shaped moraine similar to the Polson moraine ahead of it to meet with another sprawling finger of glacial Lake Missoula.

A final stop near the crest of this Elmo moraine revealed the westward-slanted orientation of rocks in the layers of sediment, testifying to the rushing flow of waters which spilt over the moraine into the Big Draw Valley following the glacial Lake Missoula flood - resulting in the shrinking of ancestral Flathead Lake as the ice sheet receeded north.

"The most important reason to have some understanding of the geology under our feet is that it is that geology which controls the resources upon which we depend. We rely on a lot of geologic resources that require a good understanding of the geology in terms of being able to find the resources as well as protect them" Hendrix said.

"In terms of education, it is imporatant to have an understanding of the world around us because it gives us a better appreciation for what we are living on and in and where we came from as far as landscape evolution and it also hoelps us to understand how these landscapes changed and to plan our landscapes accordingly," he added.

Current efforts are underway to initiate a Flathead chapter of the IAFI, to include residents from Polson, Kalispell and surrounding communities. For more information on the AIFI, visit www.iafi.org.