The California Volcano That Erupted Its Way to Being America’s 17th National Park

Lassen Volcanic National Park

On May 22, 1915, Lassen Peak blew a column of ash 30,000 feet into the sky and sent a blast of hot gas and rock racing down its slopes at 450 miles per hour.

The eruption was the climax of three years of volcanic chaos that began in 1914, when the mountain woke up after sleeping for 27,000 years.

It was one of only two eruptions in the US during the 20th century. Here’s a breakdown of what happened, and how to visit the spectacular National Park it created.

The First Rumblings

Steam burst from Lassen Peak on May 30, 1914, ending its long sleep without any warning earthquakes. For 11 months, 180 more steam blasts tore through the summit.

Each explosion made the growing crater bigger, until it stretched 1,000 feet across. Local businessman Benjamin Franklin Loomis rushed to take photos of these events.

His pictures became key records of the mountain’s changes. Steam roared from Lassen throughout spring 1915 as people came to watch, unaware of the violence to come.

The First Lava Appearance

On May 14, 1915, bright lava blocks bounced down Lassen’s sides. People in Manton, 20 miles away, saw the fiery show against the night sky.

By morning, thick, pasty dacite lava filled the summit crater. This lava contained 63-68% silica, making it too thick to flow like Hawaiian volcanoes.

The winter of 1914-15 was the first recorded El Niño year in the western United States, leaving over 30 feet of snow on the mountain. Fresh lava and deep snow set the stage for more dangerous events.

The May 19 Eruption and First Lahar

A blast on the evening of May 19 broke apart the week-old lava dome. Hot lava chunks tumbled onto the snowy slopes below. The heat quickly melted the deep snow.

A half-mile-wide mix of rock, snow, and mud raced down the northeast side. This flow, called a lahar, traveled 4 miles down the steep mountain.

At Emigrant Pass, it pushed into Hat Creek. From there, the mudflow stretched another 7 miles down Lost Creek, destroying everything in its path.

The May 19-20 Flooding Impacts

Muddy water reached lower Hat Creek valley early on May 20. Ranch houses near Old Station suffered damage from this sudden flood.

The strong current pulled trees over 100 feet tall from the ground. These trees, roots and all, became battering rams in the flow.

Ranchers ran to higher ground as their homes flooded. Some got minor injuries, but everyone lived through the night disaster.

The flood pushed 30 miles downstream to the Pit River, killing fish as mud and volcanic materials poisoned the water.

The Powerful May 22 Eruption

At 4:00 p.m. on May 22, 1915, Lassen unleashed its strongest explosion. This blast carved the larger of two summit craters still seen today.

Within 30 minutes, a huge column of ash and gas rose 30,000 feet. People in Eureka, 150 miles west, saw the mushroom cloud climb.

Benjamin Loomis had taken photos of damage from the May 19 eruption earlier that day. He left just hours before the major blast, barely escaping death.

This eruption marked the peak of Lassen’s awakening as rocks and pumice shot into the sky.

The Pyroclastic Flow Destruction

Part of the eruption column fell onto the northeast slope. This created a pyroclastic flow—a ground-hugging wave of superheated gas, ash, and rock.

The deadly mix raced down at speeds up to 450 mph with temperatures near 1,000 degrees Fahrenheit. This hot cloud destroyed 3 square miles of forest.

Trees snapped at the base or burned completely as it passed. Park officials named this bare zone the “Devastated Area,” a landscape changed forever in minutes.

The Second Major Lahar

The pyroclastic flow quickly melted all remaining snow in its path. Water turned the hot volcanic material into a fluid mudflow. This second lahar followed the same path as the first one.

The mix of volcanic material and melted snow rushed 15 miles down Lost Creek. Again, flood surged through Hat Creek Valley.

People who had barely fixed damage from the first flood now faced another wave. Smaller mudflows formed on all sides of Lassen Peak as snow mixed with hot volcanic materials on every slope.

The Widespread Ash Distribution

Ash from the May 22 eruption covered the land. Scientists found a clear layer of ash and pumice reaching 25 miles northeast from the mountain. Fine particles went much farther.

Ash fell on Winnemucca, Nevada, 200 miles east. West winds carried it across state lines. Lightweight, frothy volcanic fragments spread 30 miles from the volcano.

This ash layer helps geologists date the eruption today. The powerful blast swept away part of the lava flow that had formed just two days earlier as the mountain kept reshaping itself.

The Loomis "Hot Rock"

Benjamin Loomis found a massive boulder thrown out during the May 19 eruption. It landed in what became the Devastated Area. Days after, the boulder stayed warm to touch.

Loomis named it “Hot Rock” in his photos. Weighing about 27 metric tons, the boulder traveled miles from the summit. Half-buried in mud deposits, it stands as proof of the eruption’s power.

Loomis’s picture of Hot Rock against the bare land became valuable to science. Researchers use it to figure out which eruption caused specific damage.

The 1916-1917 Continued Activity

Though the May 22 eruption marked the peak, Lassen kept erupting through 1917. Later explosions grew weaker over time.

For years after 1915, spring snowmelt seeped into the mountain. When this water hit hot rocks below, steam explosions burst forth.

May 1917 brought strong steam blasts that created the northern crater still visible at the summit today. Justin Hammer caught one of these 1917 eruptions on film from nearby Catfish Lake, providing rare footage of the volcano’s later activity.

Visiting Lassen Volcanic National Park

You’ll find Lassen Volcanic National Park at 38050 Highway 36 East in Mineral, California. The park opens year-round, though heavy snow closes some roads from October to June.

Admission fee applies per vehicle for a 7-day pass. Join the “Eruption Trail Tour” that walks you through the 1915 eruption timeline, then drive the 30-mile park highway to see Hot Rock and Devastated Area trails.

Remember to visit the Loomis Museum at the north entrance to view original 1915 eruption photographs.

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