Winter Trekking Through Yellowstone’s Thermal and Glacial Features

Cross country skiing in one of the glacial melt-water channels on the Blacktail Plateau.

Some winter days in Yellowstone National Park are so amazing with clear blue skies and sparkling snow that they just take your breathe away. Luckily enough, I just experienced several of these kinds of days which I packed full of cross country skiing, snowshoeing, and animal watching.

One of the groomed trails that held a good snow base until about early afternoon is the Blacktail Plateau Loop. The trail follows melt-water channels that are associated with “Retreat Lake”, which was formed by the Beartooth glacial ice mass blocking the lower end of the Grand Canyon of the Yellowstone during the Pleistocene.

Rounded cobbles and boulders left behind from melt-water flow sit on the volcanic bedrock in many areas along the trail. Ski tip in the lower right for scale.
Looking back to the northwest on the Blacktail Plateau ski trail. Notice the scoop-shape of the landscape which is the result of this area being part of a glacial melt-water channel.
Calcite Springs overlook is accessible during the winter via the Tower ski trail.

The Tower ski trail provides access to the Grand Canyon of the Yellowstone area. A favorite stop of mine is the Calcite Springs overlook where the thermal springs lie south of the overlook, on the west side of the Yellowstone River and Pliocene/Pleistocene sediment and basalt are on the Yellowstone River’s east side.

 

A groomed ski trail also accesses the Upper Terraces of Mammoth Hot Springs. However, after a few days of spring-like temperatures, the snow was so melted back that I just used my snowshoes to trek through the icy slush.  Some thermal features were still covered by snow and slush, but others appeared much more vibrant against the white snow/slush blanket.

One of the fissure ridges along the upper Terraces trail is called White Elephant Back Springs and Terrace.

Aphrodite Terraces lie a short way north of the White Elephant Back Springs:

My favorite thermal feature of the Upper Terraces is Orange Spring Mound. The spring is supported by a fissure ridge and is intermittently active. Because of its low water discharge and subsequent slow growth, it has built up a characteristic cone shape.

Orange Spring Mound of the Upper Terraces in Mammoth Hot Springs.

All in all, it was perfect wintertime fun trekking around in Yellowstone. Can’t wait to get back there when the bears come back out from hibernation!

 

The Yellowstone Volcanics

Caldera boundaries of Yellowstone area eruptions over the past 2.1 million years (U.S. Geological Survey - http://pubs.usgs.gov/fs/2005/3024/)
Caldera boundaries of Yellowstone area eruptions over the past 2.1 million years (U.S. Geological Survey – http://pubs.usgs.gov/fs/2005/3024/)

Volcanic stratigraphy is hard to ignore when touring through the Teton to Yellowstone National Parks (YNP) area. Three major volcanic eruption cycles occurred during the last 2.1 million years and resulted in hundreds of feet of volcanic rock. The eruption cycles make a good basis for separating the volcanic rock units and consequently there are three major volcanic stratigraphic units. These major units consist of ash-flow tuffs that erupted at the peak of each cycle and include the Huckleberry Ridge Tuff with an age of 2.1 million years, the Mesa Falls Tuff with an age of 1.3 million years, and the Lava Creek Tuff with an age of 0.64 million years.

The type section of the Huckleberry Ridge Tuff is at the head of a landslide scarp on the Flagg Ranch, about 2 miles northeast of a bridge across the Snake River.
The type section of the Huckleberry Ridge Tuff is at the head of a landslide scarp on the Flagg Ranch, about 1 mile northeast of a bridge across the Snake River.

The type sections of the Huckleberry Ridge Tuff and the Mesa Falls Tuff are fairly accessible. The Huckleberry Ridge Tuff type section sits at the head of a large landslide about 1.5 miles south of the YNP’s south gate and 1 mile northeast of the Snake River Bridge. It’s a big landslide, so it’s easy to spot from the highway. The type section mainly contains welded rhyolitic ash-flow tuff. This huge eruptive event (one of the five largest individual volcanic eruptions worldwide) associated with the Huckleberry Ridge Tuff formed a caldera more than 60 miles across.

The type section of the Mesa Falls Tuff is a road cut along Highway 20, about 3 miles north of Ashton, Idaho.
The type section of the Mesa Falls Tuff is a road cut along Highway 20, about 3 miles north of Ashton, Idaho.

The Mesa Falls Tuff type section is really accessible as it is alongside Highway 20, about 3 miles north of Ashton, Idaho. The type section consists of airfall tuff, partially welded tuff that has an agglomeratic base. The eruption associated with the Mesa Falls Tuff formed the Henrys Fork Caldera which is in the Island Park area west of YNP.

A more detailed view of the Mesa Falls Tuff with its airfall ash overlain by partially welded rhyolitic tuff that has an agglomeratic base.
A more detailed view of the Mesa Falls Tuff with its airfall ash overlain by partially welded rhyolitic tuff that has an agglomeratic base.
Roaring Mountain lies within the Lava Falls Tuff area (photo from NPS/Peaco - https://www.nps.gov/yell/planyourvisit/norrisplan.htm).
Roaring Mountain lies within the Lava Creek Tuff outcropping area in YNP (photo from NPS/Peaco – https://www.nps.gov/yell/planyourvisit/norrisplan.htm).

The Lava Creek Tuff type section is much more difficult to access as its type section in the upper canyon of Lava Creek, about 8 miles into the backcountry of YNP. There are a couple reference sections that are easier to reach, and one is in Sheepeater’s Canyon, about 0.5 miles northeast of Osprey Falls. The Lava Creek Tuff is also readily seen in the south-facing cliffs along much of the Gibbon River. The eruption associated with the Lava Creek Tuff created the Yellowstone Caldera, the 35-mile-wide, 50-mile-long volcanic depression that dominates the present YNP landscape.

There are many more volcanic units associated with the three major eruptive cycles. But spending time looking at the major ash-flow tuff units is a good way to begin to delve into Yellowstone geology.