The Cascade Mountains stretch from southern British Columbia, Canada, all the way into northern California. Part of the famed Ring of Fire – a string of volcanoes and mountains running throughout the Pacific Ocean – the southern Cascades contain hundreds of small- to medium-sized volcanoes. This includes more than 30 volcanoes that make up California’s Lassen Volcanic National Park.
This week marks the 100th anniversary of one of Lassen’s most powerful volcanic eruptions.
Formed approximately 30,000 years ago, Lassen Peak began as a volcanic vent on Mount Tehama (also known as Brokeoff Mountain). Eroded by glaciers during the last Ice Age, Lassen’s May 19, 1915, eruption changed the area’s landscape and stirred the American imagination.
Eruptions actually began in May 1914. The first explosion generated a small crater at the summit of Lassen Peak. Over the next 11 months, steam explosions blasted out a crater 1,000 feet (300 m) long. The ultimate explosion on May 22 was the worst since Europeans settled the West in the late 1800s.
Visible from as far away as Eureka on California’s coast, the vertical eruption column rose to a spectacular 30,000 feet. Its partial collapse generated a high-speed avalanche of hot ash, pumice, rock fragments and gas that swept down the northeast side of the volcano, rushing down to Old Station, flooding lower Hat Creek Valley.
The half-mile wide lava and mudflow partially dammed lakes and creeks, completely obliterated Jessen Meadows and destroyed an estimated 5 million board feet of trees in what’s now called the Devastated Area. Ash rained down as far away as Elko, Nevada – 280 miles away.
In the early 20th century the Lassen area was home to two national monuments – Lassen Peak and Cinder Cone, the park’s second-most famous volcano which a study by the USGS and the Park Service established was formed during eruptions in 1666.
But it was Lassen’s dramatic eruption and the stunning pictures captured by local businessman and amateur photographer Benjamin Franklin Loomis that helped create the current National Park in 1916, which now encompasses 106,372 acres.
Although Lassen Peak has been relatively benign since its 1915 eruption, it is still an active volcano, says Michael Clynne, PhD., lead researcher with the United States Geological Survey (USGS). Clynne has worked with the National Park Service at Lassen since 1975.
The USGS worked with the park service to study Lassen’s geothermal activity. After Mount St. Helens erupted in 1980, this work folded into the Volcano Hazards program where the USGS reevaluated risks posed by other potentially active volcanoes in the Cascade range.
One of the surprises they found, said Clynne, is that Lassen has a large integrated volcanic system. And its amazing hydrothermals are driven by steam generated by boiling of an underground reservoir of hot water. These include fumaroles (steam and volcanic-gas vents), bubbling mudpots (hot springs with boiling mud), boiling pools, and steaming ground. All are related to active volcanism and are indications of the ongoing potential for future eruptions from the Lassen volcanic center.
“The geothermal system (whose reservoir is about 240 degrees Celsius or 464 Fahrenheit.} tells us there’s magma in the subsurface,” said Clynne, “and it could potentially become eruptable.”.
But the USGS California Volcano Observatory in Menlo Park, California, operates a sophisticated sensor network to detect any increase in seismicity, ground deformation, or gas emissions that could indicate magma rising toward the surface ahead of any future Lassen eruption.
The seismic network includes nine seismometers based around the volcano. Its information is telemetered to the Observatory and interpreted. GPS locations around the volcano monitor ground formation. They’re sensitive enough to note if the magma starts to rise and the ground’s surface is disturbed.
“We’re monitoring it,” said Clynne. “(But) it’s a wonderful natural laboratory for studying volcanoes.”
Lassen is certainly going to erupt in the future, Clynne said. “It’s an active volcano. (But) volcanoes are like people,” he said. “Each one has its own individual characteristics and behavior. (That’s) why we have to understand their history, to study what they’ve done in the past. If we know what (they’ve done), we’ll know what to expect.”
For now, Lassen and its natural wonders are to be enjoyed and appreciated. And to remember that natural cataclysm that occurred a century ago.