Lassen Peak

The unquestioned centerpiece of Lassen Volcanic National Park is the beautiful mountain known as Lassen Peak. At 10,457 feet and made up of dacite lava, Lassen Peak is the world's largest plug dome volcano. It was created nearly 30,000 years ago. The striking mountain is visible from as far away as 50 miles.

Lassen Peak is the southernmost volcano of the Cascade Range. The Cascades, the great mountain range of the Pacific Northwest, runs from about 20 miles south of Lassen Peak in California (where the Sierra Nevada Range begins) to the Garibaldi area of southern British Columbia in Canada. The name is probably derived from the "cascades" of the Columbia River which cut through the mountain range between Oregon and Washington.

The ancestor of Lassen Peak was the massive volcano known as Mt. Tehama. That peak reached an altitude of 11,500 feet and was 11 miles across at the base. The last volcanic activity associated with Mt. Tehama occurred 400,00 years ago.

Lassen Peak itself first erupted 20,000 to 30,000 years ago. It is a dome which built itself up on the rim of the ancient Mt. Tehama. The eruptions which built Lassen Peak lasted tens of thousands of years. Eventually, it reached its present altitude and bulk, the largest dome volcano in the world.

Lassen Peak was named after Danish settler Peter Lassen. It was previously known as Lassen Butte, and at one point Mount Lassen. Professor Diller referred to it as Lassen Peak, and that is the name it has been known as.

In a time before there was much knowledge of volcanoes, and before the availability of advanced scientific tools and measuring devices, it was believed by the first settlers that Lassen was extinct. However, on Saturday, May 30, 1914, a local man named Bert McKenzie witnessed the mountain returning to life. Steam and gasses escaped from the summit of the mountain. This initial eruption lasted about 10 minutes. Over the next year the volcano erupted intermittently and in a similar manner 150 times.

One year later the climax of the volcanic activity occurred. On May 19, 1915, molten lava filled the crater and poured through a notch on the northeast rim of the crater on the top of the mountain. This melted the deep snowpack and triggered a 20 foot high wave of mud, ash, boulders, and debris which ran down the northeast flank of the mountain, battering trees on the slopes and pouring down the valleys of Lost Creek and Hat Creek. It cut a swath which ranged from few hundred yards to a mile in width, , carrying 20 ton lava boulders up to 5 miles.

Three days later, an even more violent eruption occurred. A column of vapor and ash rose 30,000 feet into the air and could be seen for 50 miles in northern California. Several inches of ash fell and some ash reached as far away as Reno, Nevada. A pyroclastic flow--a blast of steam and hot gas--swept down the same flank of the mountain which had been covered by the mudflow earlier, clearing all trees, vegetation, and wildlife in its path and scrubbing the landscape bare. Five million board fee of timber were destroyed. This created the portion of the park which came to be known as the Devastated Area. The northeast flank of the mountain and the Devastated Area are shown below.

Following this great eruption, the mountain seemed to have spent much of its force. Minor eruptions continued for a couple more years, with some sizeable eruptions occurring in May and June of 1917. After 1917, the bulk of the volcanic activity ceased, with the mountain smoking and steaming only. No eruptions have been noted since 1921.By the cessation of volcanic activity in early 1921, 298 volcanic eruptions of the park had been recorded.

The eruptions of 1914 and 1915 made Lassen a national sensation and focused the attention of America on what was at that time the country's only active volcano. One of the aspects of the eruptions which attracted the attention of the nation were the photographs taken by the local man Benjamin Loomis.

The grey volcanic material which forms the spine called Lassen Peak is known as dacite. This forms from a thicker and cooler lava.

There are no glaciers on Lassen Peak or anywhere else in the park currently. However, there are some permanent snowfields at Lassen's summit and in other locations. Although not permanent, snow may be found in the Lake Helen basin (below) even into August.

The name Lassen Peak has been used for the mountain since the Whitney Survey of 1863. There were a number if Indian names for the peak, including "Fire Mountain", "Water Mountain", and "Little Shasta."