June Program: Oregon Cascades -- A Prime Volcanic Site for Adventure and Learning, Presented by Dr. Richard Tollo

By Andy Thompson, MSDC Secretary

Mount Shasta, pictured above, exemplifies the majestic and dominant presence typical of the Cascades volcanic mountains found throughout the greater Pacific northwest.  The photo’s two captions provide the title for the evening program and the overall context for the content, which bears repeating:

“The Cascades magmatic arc stretches from British Columbia to California and is perhaps best known for the large stratovolcanoes such as Mount Shasta, above, that locally dominate the scenic landscape.”

Dr. Tollo focused on the volcanoes found in northern and central Oregon which are part of the Cascades magmatic arc. By visiting and explaining selected volcanic sites throughout the region, he conveyed an understanding of the diverse volcanic processes that contributed to the formation of the Cascades as we presently see them.

The Cascades actually comprises a more-or-less linear chain of volcanoes. It is not a continuous mountain belt like the Appalachians which is orogenic, formed by the collision of tectonic plates which caused mountainous uplifts. Rather, the origins of the Cascade volcanoes are thought to represent a magmatic arc that is related geologically to off-shore subduction.

Mount St. Helens is an explosive stratovolcano volcano with a complex magmatic system. Photo by Dr. Richard Tollo.

Mount St. Helens in Washington State, shown above, erupted in 1981 and brought the Cascades to the forefront of public consciousness. “More importantly,” Dr. Tollo noted, it “was a major factor in refocusing efforts at the U.S. Geological Survey on geological hazards.” This new emphasis resulted in a decades-long explosion of excellent scientific research and discoveries which has been ongoing to this day. And, he noted, we are all the beneficiaries of this tremendous growth of knowledge about volcanoes in the Cascades range.

Simply put, Dr. Tollo’s talk took MSDC members on a spellbinding tour of major volcanic sites in the Cascades volcanic arc. He explained the geological settings of the volcanoes and examined detailed features that provided insight into the volcanic history and processes that led to and accompanied eruption events.

For many years, Dr. Tollo has conducted field work in which students and occasionally MSDC members have had personal, hands-on experience researching various geological sites.  The June 1 presentation to MSDC provided a glimpse into some of his field work within the Cascade range.

With Dr. Tollo’s generous permission, readers of this introduction can tap into this vicarious excursion by enjoying the full presentation online (lasting about 80 minutes), and hearing the question-and -answer session which followed. That’s one way of sharing in the joy of learning experienced by the GWU students, pictured below, who participated in the recent Cascade fieldwork.

Cindy Schmidtlein, MSDC’s VP for Programs, who had introduced Dr. Tollo’s presentation, told him that a few years back she had benefited greatly from an informal guidebook on Yellowstone which Dr. Tollo, years earlier, had provided for his students.  She asked if he had guide books for the sites discussed this evening. He responded enthusiastically “yes” and said the Cascades field guide was, in fact, the starting point for a new book he has been writing on field volcanology using the Cascades as its venue. He expects to finish the text shortly. “Then," he said, “we will see how its publication progresses.”

At the conclusion of the program, and the attendees’ hardy applause, Cindy and MSDC President Kenny Reynolds thanked Dr. Tollo for his excellent and very interesting presentation.

Here is the link for Dr. Tollo’s presentation:  Volcanology of the Oregon Cascades - Richard Tollo, Ph.D. - YouTube