7.8: Glaciers in the Cascades
- Page ID
- 21485
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Evidence of Pleistocene Glaciers
Although the Cascades are noted primarily for their volcanic terrain and associated hydrothermal features, volcanism and glaciation have gone hand in hand in the creation of the landscape. Today, glaciers in the California Cascades are rather limited compared with the large ice caps that covered the mountainous terrain several times during ice ages of the recent geologic past. Glaciers advanced at least five times during the ice ages of the Pleistocene Epoch, creating landforms such as moraines and outwash deposits that “overprint” much of the volcanic foundation. The alteration of volcanic rocks by hydrothermal processes facilitated glacial erosion, and glacially eroded features such as U-shaped valleys, cirques, and arêtes occur throughout the province.
At higher elevations, the main effects of Pleistocene glaciation were erosional. Glaciers deepened major valleys, removed bedrock from large parts of the landscape, and created or enlarged hundreds of lake basins. Glaciers also polished and scratched striations and grooves on bedrock surfaces (Figure \(\PageIndex{1}\)).
Glacial deposition also helped to shape the landscape of the Cascades. Glaciers and widely distributed till (a mixture of clay, silt, sand, gravel, and boulders), developed moraines, and deposited erratics (Figure \(\PageIndex{1}\)). Glacial meltwater also deposited outwash (sand and gravel) beyond the margins of glacial ice.
Modern Glaciers and Climate Change
The story of glaciation in the California Cascades is mostly a story of the geologic past. However, Mount Shasta still hosts seven glaciers: Whitney, Bolam, Hotlum, Konwakiton, Watkins, Mud Creek, and Wintun. Although there are more glaciers in the Sierra Nevada, the Cascades can claim both California’s largest glacier by volume (Hotlum Glacier) and its longest (Whitney Glacier).
By the early 2000's, a pattern of glacial retreat was evident throughout the American West and the world. However, researchers found that this pattern did not hold true for the glaciers of Mt. Shasta. Both Whitney and Hotlum Glaciers were, at the time, actually growing. Whether a glacier grows or shrinks depends primarily on two climatic factors, temperature and precipitation. The researchers reasoned that, although the climate surrounding Mt. Shasta was getting warmer each year, the winters were also getting wetter during the same period. The increased snowpack in the winter was making up for the increase in melting during the summer months. They also hypothesized, in 2006, that this trend was not likely to hold in the future. In the subsequent decades this prediction has been shown to be correct. California was struck with a prolonged drought from 2012 to 2016, and the warming trend continued, with spikes of record breaking summer heat in the early 2020's. Between 2020 and 2022, Whitney Glacier lost over a quarter of its volume. By the end of the 21st Century, it’s unlikely that any glaciers will remain in the California Cascades.
Acknowledgments
Parts of the text on this page were taken with minimal editing from sources provided by the USGS and the National Park Service, which are in the public domain. Links to the original text can be found in the reference section on this page.
References
- Arthur, D. (n.d.). California’s weather hasn’t been kind to Mt. Shasta’s glaciers. Can they survive? Record Searchlight. Retrieved May 21, 2024, from https://www.redding.com/story/news/local/2024/04/22/mt-shasta-glaciers-shrinking-as-climate-change-intensifies/73261591007/
- Garwood, J., Fountain, A., Lindke, K., Hattem, M., & Basagic, H. (2020). 20th Century Retreat and Recent Drought Accelerated Extinction of Mountain Glaciers and Perennial Snowfields in the Trinity Alps, California. Northwest Science, 94, 44. https://doi.org/10.3955/046.094.0104
- Howat, I. M., Tulaczyk, S., Rhodes, P., Israel, K., & Snyder, M. (2007). A precipitation-dominated, mid-latitude glacier system: Mount Shasta, California. Climate Dynamics, 28(1), 85–98. https://doi.org/10.1007/s00382-006-0178-9
- U.S. National Park Service. (2022, February 10). NPS Geodiversity Atlas—Lassen Volcanic National Park, California. https://www.nps.gov/articles/nps-geodiversity-atlas-lassen-volcanic-national-park-california.htm