Lake Missoula: Missoula to Thompson Falls

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay


Acknowledgement

I need to make it crystal clear that none of this is my own research. Thepictures on this and associated pages were taken on a GSA field trip in 2003 ledby Norm Smyers of the U. S. Forest Service and Roy Breckenridge of the Idaho Geological Survey, and the interpretationspresented here are largely those of Dr. Smyers and Dr. Breckenridge as presented on the field trip andits guidebook. I thank Dr. Smyers and Dr. Breckenridge for an outstanding fieldexperience.


Lake MissoulaLake Missoula
Lake Missoula Just south of I-90 Exit 101 on the west side of Missoula. There are obvious shorelines on the hillside. Also note the slump scarp just above the white building at center. The hillslope is made of Eocene sedimentary rocks.

Evaro Hill

Lake Missoula On U.S. 93 just north of I-90. Shorelines are fairly plain in this view.
Lake Missoula Left and below: shorelines are subtle but evident.
Lake Missoula Lake Missoula
Lake Missoula An unplanned stop at Evaro Hill. At high lake stand this pass would have been under 60 meters of water. 
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula

2.1 Glacial Lake Missoula Silt

Lake Missoula The best view of laminated Lake Missoula silt along U.S. 93 is unfortunately in a road cut along a notoriously unsafe highway with narrow or no shoulders.
Lake Missoula At the most accessible safe outcrop, the silt is pretty much non-laminated. It is also pure white in contrast to the pink silt near Alberton. Below are laminated silts on adjacent private land.
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Below: views southwest across the valley.
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula

National Bison Range and Mission Range

Lake Missoula Between Ravalli and St. Ignatius, looking northeast at the Mission Range.
Lake Missoula Left and below: looking west into the National Bison Range. The Belt quartzite here is steeply dipping, so horizontal features on the hillsides must be shorelines.
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Below: especially well developed shorelines on the east side of U.S. 93.
Lake Missoula Lake Missoula
Lake Missoula Left and below: views of the Mission Range near St. Ignatius.
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula

Left: map of the Mission Range. This is a marvelous range, which owes its grandeur to a fault scarp. The fault is recently active and considered a potential source of large earthquakes. The Mission Range Fault and a couple of cross-cutting faults at the south end of the range are in purple. Not all faults are shown.

Below: panorama of the Mission Range. This end of the range has glacial features to rival Glacier National Park.

2.2 Pingo Scars

Lake Missoula Pingos are raised mounds formed in permafrost terrain by freezing of ground water. When they melt and collapse they leave round holes with raised rims and slump textures in the rims. Large pingos on the map above are highlighted in yellow. Left and below are views of some of them. Large ones are water filled, smaller ones are often dry.
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Left: a small dry pingo scar.

Below: views of the Mission Range.

Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Looking north along the Mission Range scarp.

2.3 Polson Moraine and Flathead Lake

Flathead lake is impounded by two moraines. The south end of the lake isdammed by the Polson moraine. Below is a panorama looking north from just abovethe town of Polson. At extreme ends of the panorama is the moraine. At center inthe distance is Flathead Lake, and the scarp of the Mission Range is at right.On the map above the moraine is gray and the roads where the pictures were takenare in yellow.

Lake Missoula
Lake Missoula South side of the Polson Moraine from U.S. 
Lake Missoula Road cut and gravel pit in the moraine just south of Polson.
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Left and below: south side of the Polson Moraine.
Lake Missoula
Lake Missoula Left and below: vies of Flathead Lake and the moraine from above Polson.
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Left and below: views between Polson and West Arm.
Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula

2.4 Big Arm Moraine

Lake Missoula Left and below: the western arm of Flathead Lake is blocked by the Big Arm Moraine.
Lake Missoula Lake Missoula
Lake Missoula Left and below: looking back toward Flathead Lake from the summit of the moraine.
Lake Missoula Lake Missoula
Lake Missoula  
Lake Missoula  
Lake Missoula Lake Missoula
Lake Missoula Road cut in moraine
Lake Missoula Moraine topography
Lake Missoula Large gravel pit at the summit of the moraine
Lake Missoula Gently sloping fan surface west of the moraine.

Route 28

Lake Missoula These pictures show shorelines and lake sediments between Flathead Lake and Hot Springs.
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Left and below: outcrops of lake sediment on the valley floor.
Lake Missoula In the two views below, the peaks of the Mission Range can be seen above the tops of the hills in the middle distance.
Lake Missoula Lake Missoula
Lake Missoula Some fairly obvious shorelines accented by trees.

2.5 Markle Pass and Camas Prairie

Lake Missoula Markle Pass contains a tract near the summit that is a fairly credible imitation of scablands terrain, except that it's in quartzite rather than basalt.
Lake Missoula Closed depressions like this one occur in the Scablands and have been called "kolks." They have been attributed to intense eddy action and likened to gigantic potholes.
Lake Missoula  
Lake Missoula Below: looking north to the scabland and the large kolk right of the road.
Lake Missoula Lake Missoula

Panoramic view of the pass from the south.

Lake Missoula

Lake Missoula Looking south from the pass. The low ripples at center are giant current ripples. I remarked that they didn't look very convincing. It looked like slightly gullied terrain like you might see anywhere. That set me up nicely. "Wait until you see the surface materials."
Lake Missoula
Lake Missoula
 
 
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula
Lake Missoula
 
Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
 
 
  Lake Missoula
Lake Missoula
Lake Missoula Left and below: looking back toward Markle Pass. The low ridges running across the picture below the pass are current ripples.
Lake Missoula Lake Missoula
Lake Missoula Left and below: views of the ripple marks south of Markle Pass en route to Perma.
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula

I shouldn't leave this locality without duly noting questions raised by sometrip members who saw real problems with how to get deep water moving at suchhigh speeds. The physical evidence leaves little doubt that it did happen, buthow? Large reservoirs that drain catastrophically generally don't achieve highcurrent velocities far back from the outlet. The outlet at Lake Pend Oreille wasquite wide and perhaps dropped lake levels rapidly enough to cause high speedflow in constrictions. Perhaps, too, the highest speeds occurred at somecritical point in the drainage when lake levels dropped low enough to make constrictionsmost effective. Could ice rafted by the floods have temporarily blocked somechannels, creating local mini-outbursts?

2.6 Gulch Fills

Lake Missoula Flathead River near Perma
Lake Missoula Curious structures resembling earthen dams occur high up in side valleys in this area. Bretz called these "gulch fills." These were eddy deposits created during the lake drainage.
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Above: one of the clearest gulch fills about 4 miles NW of Perma Below: Flathead River
Lake Missoula Lake Missoula

Clark Fork River

Views between Paradise and Thompson Falls

Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula
Lake Missoula Lake Missoula

2.7 Eddy Narrows

Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula
Lake Missoula

Geological Society of America Channeled Scablands Trip, 1994

Spokane to Soap Lake
Soap Lake to Chelan
Chelan to Othello
Othello to The Dalles
The Dalles to Seattle

Geological Society of AmericaGlacial Lake Missoula Trip, 2003

Spokane to Missoula
Missoula to Thompson Falls

Other Missoula Floods Pages:

Wallula Gap
Frenchman Coulee


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Created 9 April 2003, Last Update 07 June 2020