About the Site
Lassen Volcanic National Park (10)  


Park History

Lassen Peak

Lassen Peak Summit

Chaos Crags

Manzanita Lake



Park Mountains

Sulphur Works

Volcanic Remnants

Southwest Area

Park Road


Plants & Animals


Volcanic Remnants

Lassen Volcanic National Park is filled with the evidence of past volcanic activity.

Devastated Area The two eruptions of May, 1915, created a vast area of devastation within the Lassen area. The first eruption created snowmelt and a mudflow which scoured forests and flowed over other topographic features on the northwest face of Lassen Peak. The second resulted in a pyroclastic flow which swept over the same area which had been subject to the mudflow. The area affected in this way is known as the Devastated Area, and it covers a 3 mile long by 1 mile wide area.

This view of the Devastated Area all the way to the peak show the degree to which forests, meadows, and various types of vegetation has reclaimed what was once a barren landscape. Aspens are among the first trees to recolonize an area such as this, but as can be seen full reforestation is eventually accomplished.

The May 19, 1915, mudflow which first cleared the Devastated Area moved at a slow and steady pace of several miles per hour. The mud flowed more like mortar than water. Farmers who were warned of its coming were able to outrun the flow and escape. The depth of the mudflow was surprising, with marks on the trees reaching as high as 18 feet above the ground. The mudflow carried huge rocks which were eventually deposited in various places in the devastated area, such as the one shown below.

The mudflow which resulted from the May 19, 1915 eruption battered trees in the area through which it flowed. In many cased bark facing the direction of the oncoming flow was knocked off, but many trees survived. The pyroclastic blast of May 22, however, cleared the landscape of existing trees.

The park maintains a nature trail through a portion of the Devastated Area which includes informational signs such as the one shown below describing the events which created it and the features which can be seen even today, over 90 years later.

Another portion of the nature trail is shown below.

Hot Rock Several large rocks carried by the 1915 mudflow have been known as the "Hot Rock." The best known of the "Hot Rocks" is this rock, located next to the park road north at 8164 feet and a little east of Lassen Peak. It is one of the most popular volcanic remnants and tourist attractions. The rock weights 300 tons, although half of the rock itself is buried under the ground. It is composed of dacite lava and white feldspar crystals. It was carried to its present position during the May, 1915, eruption, from an original position 4 1/2 miles away.

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  • All photographs ©Patrick Holleran, Shannon Digital Imaging, 1994-2012

  • Commercial use of the images contained in this document without express written consent is strictly prohibited.

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