{"id":8711,"date":"2025-01-30T08:30:00","date_gmt":"2025-01-30T15:30:00","guid":{"rendered":"https:\/\/www.voile.com\/blog\/?p=8711"},"modified":"2025-01-28T09:47:49","modified_gmt":"2025-01-28T16:47:49","slug":"a-geological-ski-tour-of-mt-shasta","status":"publish","type":"post","link":"https:\/\/www.voile.com\/blog\/a-geological-ski-tour-of-mt-shasta\/","title":{"rendered":"A Geological Ski Tour of Mt. Shasta"},"content":{"rendered":"

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The young summit looked like a volcanic rock fortress, a specter surveilling the crater below, covered in rime but otherwise untouched by time. According to the map, it was only 600 ft. or so above where we stood, but it appeared a thousand times taller before us. <\/strong><\/p>\n\n\n\n

Just before midnight, Nathan and I began the drive up the long, curving road from the town of Mt. Shasta, California to the Bunny Flat trailhead at the base of Mt. Shasta, some 40 miles or so south of the California-Oregon border. We spent the better part of the previous hour watching the 14,163-foot tall mountain in the starlight at Sisson Meadow park before beginning our automobile approach. We drove in separate cars, but I could feel our joint anticipation mounting as we neared the base of the giant. <\/p>\n\n\n\n

A Volcanic History<\/h2>\n\n\n\n

As far as recent volcanic history goes, in the last 10,000 years, Shasta has erupted at a rate of once every 600-800 years, making it the second most active Cascade volcano, behind Mt. St. Helens. As a student of geoscience from the Intermountain West, I was wide-eyed at my recent personal discovery of real-life volcanoes here in the Western U.S. I wanted to get close to them. I have since taken to reading about the Cascade volcanoes in Stephen Harris\u2019s \u201cFire and Ice\u201d and \u201cFire Mountains of the West\u201d, two books whose depth of geologic insight informed my understanding of Shasta as presented here. <\/p>\n\n\n\n

The Cascade volcanoes are arranged in a roughly north-south arc from northern California up to British Columbia in Canada. These volcanoes formed as a result of hot earth material upwelling from the diving down of the Pacific tectonic plate underneath the Pacific coast of North America. Of the 20 or so major Cascade volcanoes, Mt. Shasta is second in height only to the giant Tahoma (Mt. Rainier, 14,411 ft.) to the north in Washington State. It is, however, the largest stratovolcano (cone volcano with steep sides, the kind you\u2019d probably envision if asked to draw a volcano) in the Cascades by volume, composed of 85-90 cubic miles of lava material. The mountain is exceptionally prominent, visible for many miles surrounding it. It drew us in from great distances without its massive stature seeming to change at all. <\/p>\n\n\n\n

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The Science of Stratovolcanoes<\/h2>\n\n\n\n

Stratovolcanoes form tall, steep structures due to the high viscosity of the lava material. In general, lavas with more silica are more viscous and are lighter in color when cooled, like andesite or rhyolite; Lavas with less silica are less viscous and are darker in color when cooled, like basalt. A highly viscous lava will stick and flow more slowly, like molasses, piling up on itself before cooling and becoming rock. On the other hand, a lava of low viscosity flows more freely and spreads out across a greater area. Shasta gets its massive height and stratovolcano classification from eruptions of more silica-rich, viscous lavas. Shasta is not just one volcanic cone erupting highly viscous lava, but four distinct cones piled on top of one another. <\/p>\n\n\n\n

Ancestral Mt. Shasta started growing over half a million years ago. Though it potentially stood as high as modern-day Shasta, little trace of its original structure can be found today, but grayish andesite lava rock found near McBride Springs can be dated to about 593,000 years ago. Between 380-300,000 years ago, the northwest side of ancestral Shasta completely collapsed. The debris from this event flowed through and cleared out what is now the expansive Shasta Valley, where the Shasta River flows. It left behind material that now appears as hills, ridges, and mounds in the valley. Some say it was likely the largest landslide event in North America\u2019s geologic history. <\/p>\n\n\n\n

Starting the Climb<\/h2>\n\n\n\n

Spring was in full swing when Nathan and I arrived. Recent storms brought new snow to upper elevations and shrouded visibility with cloud cover in the week leading up to our attempt, but we had ourselves a window of mostly clear weather. It was late May of a historic year of snowfall, so the white stuff lingered at lower elevations on the mountain, allowing us the distinct privilege of stepping from a dry parking lot directly onto snow to start ski touring at 6,900 ft. <\/p>\n\n\n\n

Once parked at Bunny Flat, we filled out our permits and paid our summit fees before retiring, giddily, to the back of our vehicles to get some restless shut-eye before an early morning departure. Our intended climbing route was Avalanche Gulch; our intended ski objective was the West Face. By 4:45 AM, Nathan and I were dressed in our ski touring gear and putting skins on our skis as we sipped hot coffee. Thirty minutes later,  we scrambled up the side of the head-high snowbank just around the corner from the trailhead outhouse and stepped into our toe pieces to begin our climb. <\/p>\n\n\n\n

In the calm of predawn, we skinned along a strip of snow through trees, parallel to a shallow ravine, alternating between lightly side-hilling on one side of the creek and the other. We encountered a man from New Mexico who began his quest around the same time. He spoke of the mystical pull of this mountain which beckoned him to be there exactly then. <\/p>\n\n\n\n

Before long, the forest of firs and pines thinned out. The immense majority of the mountain appeared before us above the treeline as we entered Avalanche Gulch proper, the largest glacially carved valley on the mountain, though no glacier resides there now. Shasta lies east of the Klamath Range which captures most of the possible precipitation from moisture blowing in from the Pacific Ocean. This precipitation deficit gives Shasta its sparse, stunted forests compared to other Cascade volcanoes like Hood, also to its north. It also means that the geology of Shasta itself is subjected to fewer of the erosional forces of falling water, snow, and ice, allowing the mountain to retain more of its \u201coriginal\u201d appearance than the others of its order. <\/p>\n\n\n\n

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To our right stood the oldest structure of modern Mt. Shasta, the Sergeant\u2019s Ridge cone, which grew over a period of eruptions and material upwellings over 100,000 years ago. Our route was straight up the gut of Avalanche Gulch, up to a saddle at above 12,000 ft; and then up and over Misery Hill to the summit. The route to Misery Hill lies entirely on Shasta\u2019s second volcanic cone, the Misery Hill cone, which, at 25,000 years old, is much younger than the Sergeant\u2019s Ridge cone. It takes its name from the aptly named false summit that awaited our high elevation slogging.<\/p>\n\n\n\n

As we climbed higher, the slope got steeper. The snow surface above treeline was frozen slick and hard, and sun-cupped. Sun cups are a result of portions of the snow surface melting at different rates. This is likely caused by dirt in depressions melting faster and deepening the depression, or due to mild winds cooling the ridges between melting depressions. Sun cups form in grids across the snow surface, creating a widespread, non-uniform surface. Needless to say, when frozen like this, they are an absolute pain to gain enough purchase on to skin up. Nathan and I paused to watch the sunrise colors dance across the southern horizon, glimpsing the shadow of Shasta itself cast across the clouded lowlands. We decided to put on ski crampons to make the going easier over the icy and deeply dimpled snow. At the crest of a knoll, a break in the clouds allowed me the opportunity to snap a photo of another volcano, Lassen, visible in the distance to the east. I removed my glove, accidentally dropped it, and watched as it skittered, just out of reach. It gained speed, sliding down through the basin Nathan and I just climbed, across another flatter section of slope, and over another knoll and continued tobogganing down Avalanche Gulch, never to be seen again. Thankfully, we had an extra pair. <\/p>\n\n\n\n

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The Challenges of Avalanche Gulch<\/h2>\n\n\n\n

At around 11,500 feet, about four and a half hours into our climb, we Voile-strapped<\/a><\/strong> our skis to our packs A-frame style, put crampons on our ski boots, and began booting up the still shaded and firm slope up to the head of Avalanche Gulch in a series of switchbacks. My HyperVectors<\/a><\/strong> felt light, but sturdy on my backpack. We made our transition next to a frozen pile of day-old avalanche debris, a reminder of why we had better keep moving while the sun was still shielded from the aspect we were climbing. Another hazard existed here, though: Rockfall. Above us was a stout, orange headwall, about 200 feet thick. The slope was littered with fragments of the porous lava rock pumice that had evidently come loose from the looming feature, falling during warming events and refreezing into the matrix of the surface snow overnight. The orange band of rock is the Red Banks tephra, a rapidly cooled lava rock from one of Shasta\u2019s most explosive periods, starting about 9,700 years ago. <\/p>\n\n\n