#16 - Mission Reservoir in Western Montana - A Moraine-Dammed Lake

This is Mission Reservoir in western Montana - about 50 miles north of Missoula. St. Ignatius (pop. 842) can be seen in the distance. The reservoir is actually a moraine-dammed lake formed by a valley glacier during the last ice age. It has been modified to serve as a reservoir.

The “lateral moraines” were deposited along the sides of a valley glacier (a.k.a. alpine glacier) during the last ice age. The moraines are the curved ridges along the sides of the reservoir. These forested ridges consist of rock material that the glacier removed from the mountains in the upper part of the drainage basin, high above the lake. Over the thousands of years since the moraine was formed, soil has formed on top and trees have taken root.

Right: Aerial photo of Mission Reservoir taken several years ago by Lawrence Dodge of Big Sky Magic Enterprises.

Below: This is similar to what the Mission Reservoir area probably looked like when the alpine glacier filled the drainage.

Rock material that has been transported and deposited by glaciers is called "till". As the glacier formed, rocks became stuck to its bottom and sides. Then as the ice flowed toward the valley floor, these rocks scoured away even more of the mountain’s surface. The glacial ice flowed to the position marked by the location of lake where it melted and dropped the rocks. For thousands of years, snowfall continued to replace the ice as it flowed away from the mountain tops. This "conveyor belt" took much of the mountain with it, forming the moraines. Much of the till deposited at the end of the glacier was washed away as the ice melted, so some of the original "end moraine” is missing. Since the end of the last ice age (10,000 years ago), soil has developed on the moraines and trees have taken root.

Geologists describe till as “unsorted” because it is made up of all sizes of rocks. This characteristic helps geologists distinguish materials deposited by glaciers from those deposited by running water, which tends to deposit different sizes of rocks in different areas.

Terms: lateral, till

Related Links . . .

1. CLICK HERE to access the blog post and photo tour of the hike I did to get the photo of Mission Reservoir.

2. CLICK HERE to watch a 3-minute drone video of the Mission Reservoir.

3. CLICK HERE to see a nice photo of Lake Wallowa in northeastern Oregona - another great example of a moraine-dammed lake.

Borah Peak Fault Scarp in Idaho formed during 1983 Quake

The thin tan line in this photo is the Lost River Fault Scarp, which runs for over 20 miles along the base of the Lost River Range in central Idaho. The scarp formed as result of a 6.9 M earthquake that occurred at 8:06 am on October 28, 1983. The quake was named the “Borah Peak Earthquake” because it happened near Borah Peak (12,662 ft.), the highest mountain in Idaho - the one on the left in this photograph. The photo was taken along the road to the Birch Springs Trailhead where hundreds of hikers come every year to begin their ascent of Borah (known locally as Mt. Borah).

The Lost River Range is a fault-block mountain range on the northeastern edge of the Basin and Range Province. Like Basin and Range Mountains in other states such as Utah and Nevada, these mountains formed one earthquake at a time over millions of years. During the 1983 quake the valley side of the fault dropped 9 feet and the block that includes the Lost River Range rose 6 inches, leaving the offset (scarp) shown in the photos.

The epicenter was located along the fault somewhere between the small towns of Mckay and Challis. Although it was the most energetic earthquake in the lower 48 since the 1959 Hebgen Lake Earthquake in southwestern Montana, there were only two deaths. Two children (ages 6 and 7) were killed in Challis when a brick wall collapsed on them as they walked to school. Shaking was felt in eight states and two Canadian provinces, lasting from 30-60 seconds.

Below: This photo, taken by Bruce Railsback of the University of Georgia, shows a person standing below the Lost River Fault Scarp (near bottom, center of photo). Bruce took the photo in in 1987, four years after the earthquake happened.

Links . . .

Newspaper coverage by the Idaho Statesman

Basin and Range Province (Wikipedia)

Climbing Mt. Borah (aka Borah Peak)

Fault-Block Mountains (Wikipedia)

Animation of the Night Sky at Your Location

CLICK HERE to go to Timeanddate.com, set the site to your location (or a nearby city), scroll down to the "Night Sky Map", select a planet to watch, and then click on the play arrow (or FFWD arrow, or scroll bar). You can pause and scroll over stars or other planets to see their names. Pretty dang cool if you ask me! The site provides plenty of other interactive astronomy animations to fiddle around with as well.

Below: This screen shot is an example of what you will see - except it will be in motion. NOTE: The site resets at noon every day, so the best time to check is afternoon.

Under Construction

#130 - Kelvin-Helmholtz Clouds Caused by Wind Shear

The right place, at the right time.
This photo of an amazing Kelvin-Helmholtz cloud was taken on January 26, 2019 by Hannah Martin, one of my freshman Earth Science students at Helena High School. She snapped the photo from the Helena Valley, looking west - Mount Helena can be seen on the left, and the distant horizon marks the Continental Divide. Also known as "fluctus" or "billow" clouds, they were named after Lord Kelvin (1824-1907) and Hermann Von Helmholtz (1821-1894) who identified the type of instability responsible for the unique waves. Such clouds are fairly rare, and may only last for a few minutes.

Like wind across water.
The waves form at the boundary between layers of air that have different densities and wind speeds (wind shear). Air in the layer above the cloud is moving faster than air in the layer containing the cloud. Development of waves on the cloudy layer is similar to what happens when waves form on the ocean as wind blows across the water. In the photo the wavy layer is more dense than the clear air flowing above it - just as water is more dense than air blowing over its surface.

Clouds provide a "visual".
The type of motion that causes the wave pattern is actually not that uncommon in the atmosphere, although we usually don't see it. In order for us to see it, clouds must be present in the lower layer (as they were when the photo was taken). We can't see clear air, but we can see clouds. One of the nice things about clouds is they provide clues about the type of motion currently happening in the atmosphere. Want to know more? - Watch the 4.5-minute video below, which includes a great demo.

Term for students to define: wind shear

1. Article - More about KH Clouds

2. Another good article about KH Clouds

Enter your address to see where you would have been millions of years ago.

This is a fantastic interactive visualization that was created (and is maintained) by Ian Webster. Once the site opens, enter your address in the box in the upper left, then select the time (in Earth's history) near the top of the web page. To see more of Ian's work, go to ianww.com.

Thanks to Rick Dees for showing me this!