Mapping the Hazards Lurking Beneath the Cascade Volcanoes

If you’ve stood on a ridge in the Pacific Northwest—or many other places around the world—and gazed at a snow-capped peak in the distance, you may have been looking at a volcano. While volcanoes that aren’t currently erupting often seem like distant features of the landscape, the risks they pose are very real, and the information required to mitigate those risks is not always known. Across the globe, researchers still lack basic data about where magma is stored beneath the surfaces of volcanoes, how it moves before an eruption, and what warning signs to watch for.

Penny Wieser, a volcanologist and assistant professor of Earth and Planetary Science at UC Berkeley, is working to change that. Using cutting-edge geochemical tools her lab is helping build the foundational knowledge—and global toolkit—needed to better anticipate eruptions and protect the people who live in their shadow.

Her newest project focuses on the Cascade Range, a line of more than a dozen volcanoes stretching from northern California to Washington, including Mount Rainier, Mount Shasta, and the Three Sisters. Collectively, they hold the dubious distinction of being some of the most dangerous volcanoes in the United States. Yet, compared to their more active counterparts in places like Hawaii or Iceland, most of them remain poorly understood.

“We have very little data on many of these volcanoes,” says Penny Wieser. “They’re not erupting frequently, but that doesn’t mean they’re not hazardous.”

With support from the 2024 Heising-Simons Faculty Fellows award, Wieser’s lab is beginning a multi-volcano comparison across the Cascades, using advanced chemical and mineralogical analyses to probe where and how magma is stored beneath the surface of each volcano—and how that has triggered past eruptions in the mountain range. 

Mapping Magma

Before turning her attention to the Cascades, Wieser built her expertise on very different volcanic systems. Much of her prior work has focused on island volcanoes like Hawaii’s Kilauea and Mauna Loa. While carrying out field research at Kilauea during graduate school, Wieser realized just how much more there is to learn about what was happening below volcanoes.

“What my research tries to understand is where is the magma stored beneath a volcano,” she says. “As volcanoes wake up and you start getting earthquake activity or ground deformation, it’s really important to have a map of the plumbing system beneath the volcano to interpret any unrest.”

Frustrated with the limitations of traditional techniques, Wieser has developed new ways of analyzing volcanic materials to determine their precise origins underground. 

A Dangerous Quiet

While the 1980 eruption of Mount St. Helens remains seared into public memory, many other Cascade volcanoes have been quietly accumulating risk. Mount Rainier looms over the Seattle metro area and, during past eruptions, is known to have generated destructive volcanic mudflows. If triggered today, those mudflows could reach populated valleys with little warning. Mount Adams and the Three Sisters have also shown recent signs of magma movement but lack the monitoring infrastructure needed for accurate forecasting.

According to the United States Geological Survey  “National Volcanic Threat Assessment” that ranks  the most hazardous volcanoes in the United States based on not only their likelihood of activity, but also their potentially dangerous impacts, five of the top ten ranking volcanoes were in the Cascade Range. 

“The threat isn’t just in how likely a volcano is to erupt,” Wieser says. “It’s also in how close people are to it, and how much warning we can realistically give.”

Now, Wieser plans to analyze erupted crystals and lavas collected from the Cascades, establishing how deep magma is stored beneath each volcano and how it has moved and mixed prior to eruptions spanning the last 10,000 years—information recorded in the chemistry of crystals within lava rocks. 

A Bold, Broad Effort

The Heising-SImons Faculty Fellow award is enabling Wieser to pursue broad questions and tool development that might not typically be supported by a short-term, highly focused research grant. Different volcanoes in the Cascades will be assigned to different members of her team for in-depth study. Graduate student Sarah Shi, for instance, is focusing on Mount Rainier, while postdoc Annika Dechert is leading efforts at South Sister, a volcano that has been gradually inflating—suggesting possible magma accumulation beneath the surface.

One goal is to determine whether Cascade volcanoes share common eruption triggers—such as fresh injections of hot magma—or whether each behaves according to its own rules. 

“Right now, we just don’t know,” Wieser says. “Any information we gather will be a big step forward.”

The team is also coordinating fieldwork with the U.S. Geological Survey and collaborating with a network of scientists to obtain volcanic samples. In the lab, they’re developing standards and calibration tools that will benefit the entire volcanology community, enabling more accurate measurements of water, carbon dioxide, sulfur, and chlorine in volcanic glasses—components that help shape eruption style and impact. 

“We’re not just studying the volcanoes,” Wieser says. “We’re improving the tools everyone uses to study them.”

Science That Could Save Lives

Although Wieser’s work is rooted in basic research, the implications for public safety are immediate. By reconstructing how past eruptions unfolded, her team aims to establish warning signs—such as ground inflation or shifts in stream chemistry—that signal when a volcano is becoming restless.

“If we know that, say, new magma was injected five years before the last eruption, we can use that as a baseline when we detect similar signals again,” she explains. “That’s potentially lifesaving information.”