Mount Rainier towers above the landscape southeast of Seattle, Washington, with a summit elevation of 14,410 feet. An iconic image of the Pacific Northwest, this majestic glacier-covered mountain provides a dramatic backdrop for hundreds of thousands of people living in the surrounding region. The forests, glaciers and steep rocky slopes on the mountain also provide a popular playground for hikers and mountaineers. The beauty of Mt Rainier masks the fact that it is an active volcano with a high probability of erupting again in the not-too-distant future. This could happen in 10 years, or 100 years or 1,000 years, or even longer; no one knows.
Recently I came across a fascinating blog post called The Penitentes of Mt Rainier by Albert. This post is on a blog site called Volcano Café (https://www.volcanocafe.org/), which was established to share information about volcanic activity around our planet and beyond. The link to this post is below, but first I want to share a few especially interesting things I learned from Albert’s post. (A few facts about Mt Rainer are in my Mountains of Fire in the Pacific Northwest blog post published in May 2020, as well as in the article 5 Important Questions and Answers About USA Volcanoes that I share with new website email subscribers.)
First, dangerous lahars have occurred — and will continue to occur — on Mount Rainier. When an eruption heats the ice and snow blanketing a tall volcano, the water and soil that start to flow down the mountain can turn into lahars – volcanic landslides or mudflows that speed downward, covering the landscape with layers of cement-like sediments that can be hundreds of feet thick.
Here is the new information I learned: about 500 years ago a major lahar streamed down from Mount Rainier, and there is no evidence that this was caused by an eruption. In fact, there is some evidence that large lahars may cause eruptions, as the weight of soil and rock removed from mountain slopes allows subsurface pathways to open and magma to rise to the surface and erupt. Scientists believe a lahar could happen at any time along the steep sides of Mount Rainier – and towns in the river valleys surrounding the mountain will be in the greatest danger. Such an event could also signal the start of a new eruptive period. Hopefully, this will only happen far into the future.
Second, penitentes are found on the high slopes of Mount Rainier. These are unusual blade-shaped snow and ice formations that are elongated and point toward the sun. A field of these forms resembles a crowd of kneeling people doing penance, with tall white hats like those worn by some Catholic religious orders. Although I had no idea that these were found on Mount Rainier, these features are vaguely familiar to me because they also occur in the Andes Mountains (thus, I had to share the fabulous photo from the Atacama Desert, below).
Penitentes typically form on high altitude glaciers and in very dry air, especially in tropical latitudes. On Mount Rainer they grow up to about 3 feet in height, but in the Andes Mountains they can grow to 15 feet or more. Spectacular! And if this isn’t remarkable enough: the spacecraft New Horizons that flew near Pluto about 5 years ago sent back images showing a “bladed terrain” that is interpreted as penitentes formed from methane snow. Amazing!
To learn more about glaciers, lahars, ice caves, penitentes, and other intriguing information, please read Albert’s post The Penitentes of Mount Rainier here: https://www.volcanocafe.org/the-penitentes-of-mount-rainier__trashed-2/ . As a bonus to the great descriptions of Mt Rainer, you will also see the clever Volcano Café website banner. It shows open shelves with a display of bottles and a fabulous view of mountains beneath a color-streaked sky – definitely a place I wish I could visit someday (except it doesn’t exist, I know).
Mount Rainier reflected in a small lake at the top of the Tatoosh Range, 2006, US National Park Service; https://commons.wikimedia.org/wiki/File:Mount_Rainier_and_lake_reflection.jpg
Penitentes under the night sky of the Atacama Desert; by ESO/B. Tafreshi (twanight.org) – http://www.eso.org/public/images/potw1522a/, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=40721308
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Who knew? So was the Mt St Helens eruption in part a lahar? Thanks Roseanne.
Yes! The huge landslide of soil and rock that broke away from the side of Mount St Helens mixed with snow, ice and water to create lahars. These flowed down river valleys and emptied into the Colombia River, 17 miles away! Yikes! Thanks for the note Steve.