Hirt's workshop details differences between local volcanoes

Staff Writer
Mount Shasta Herald
By volume of eruptive material, Medicine Lake is much larger than Mount Shasta, though it is much flatter and does not look as impressive. Bill Hirt, Ph.D, will discuss why the Mount Shasta and Medicine Lake Volcanoes are so different on Thursday, Sept. 12, at 8 p.m. at Mt. Shasta Sisson Museum.

On Thursday, September 12, at 8 p.m., Dr. Bill Hirt will be giving a talk at Mt. Shasta Sisson Museum comparing Mount Shasta and the Medicine Lake volcanoes. These are the largest volcanoes in the southern Cascades Mountain Range and are only 30 miles apart, yet they couldn't be more different.

Most people can readily identify Mt. Shasta, though few recognize Medicine Lake Volcano. Compared to Mt. Shasta, Medicine Lake Volcano is long, low, and undramatic. Its broad slopes are covered by thin flows of runny basalt like those seen in Hawaii.

Despite having a volume roughly twice that of Mt. Shasta, the pancake-shaped Medicine Lake Volcano only rises to a summit elevation of about 7,000 feet and its flanks are dotted with both cinder cones and domes of glassy rhyolite.

In contrast, Mt. Shasta’s steep slopes define a graceful cone that is readily seen from miles around. This strato-volcano has five glaciers and rises to a summit elevation of over 14,000 feet. It is built of multiple layers of different kinds of eruptions, from gray andesite and dacite lavas that form thick, stout flows to layers of shattered rock produced by turbulent pyroclastic flows.

According to Hirt, “Although both volcanoes are linked to the Cascadia subduction zone, their locations mean that the melting processes that produce the erupted lavas are quite different. I will explore these differences and how they influence the eruptions that have shaped each volcano. We will also discuss the potential hazards from living near these volcanoes.”

Hirt has been interested in geology and volcanoes for a long time.

“I started collecting rocks and minerals when I was 5 or 6 years old, inspired by a little boxed set of samples my grandmother brought me from Las Vegas.A friend of my father who taught at the local community college was kind enough to give me some more samples and a mineralogy textbook when I was in fifth grade. After that, there was no looking back!”

Hirt went on to graduate from UCLA and then earned his Ph.D. in geology at U.C. Santa Barbara. Hirt joined the faculty at College of the Siskiyous in 1991.

When asked why people should be interested in geology, Hirt responded, “As a friend of mine says, ‘Geology is the base layer of the natural world.’ If we want to understand how environmental changes that are underway today compare with those that have occurred in the past – and how current changes may play out in the future – geology can offer important insights.”

This event is part of a series of talks about this area and the suggested $5 donation is a fundraiser for Mt. Shasta Sisson Museum. The Mt. Shasta Sisson Museum is a tax-exempt, non-profit organization with an all-volunteer staff that installs new exhibits to share the stories of the Mount Shasta area for its community members and visitors. It is located at 1 North Old Stage Road.

Mt. Shasta Sisson Museum hours for September are Monday through Thursday, 1 p.m. to 4 p.m. and Friday, Saturday, and Sunday, from 10 a.m. to 4 p.m.