Lassen Volcanic National Park

On a trip to Lassen Volcanic National Park, you might see mud pots, and they might stink. A mud pot is a hot spring boiling with mud. Mud pots are usually sulfurous, so they tend to smell like rotten eggs. Boiling mud springs are just one of the interesting features in the 165-square-mile park. This area in the northeastern corner of California became a national park in 1916, a year after Lassen Peak spewed a mushroom cloud of ash that was seven miles high.

Like many places in California, the land in the park is still active. Even though Lassen Peak stopped actively erupting in 1921, small amounts of steam still rise from its vents. Hot springs and mud pots in the park also serve as reminders of the heat and activity just below the park's surface.

The park today is the result of millions and millions of years of changes. If you wanted to visit the park about 70 million years ago, you would need to be good at holding your breath! The whole area was covered by an ocean and served as a seaway connecting two larger bodies of water—one in California, and the other in Oregon. Over the course of time, activity under Earth's crust repeatedly bent, folded, and broke the rocks on the surface. Lava began to rise to the surface. Volcanoes sprouted, and for a period of time, lava and ash built up on Earth's crust, forming the western Cascade Mountains.

About 11 to 12 million years ago, the High Cascade Mountains rose up from the bent crust of volcanic rock. More volcanoes formed over the next 10 million years. The Great Ice Age hit, and still more volcanoes formed. Two to three million years ago, volcanic mudflows oozed over the High Cascades, leaving behind a mess of debris. And, of course, there was more volcanic activity. Basaltic lava poured into some areas of the park, while other areas were being covered with andesitic lavas. A big hunk of rhyolite pushed out of Earth into one area, and another hunk of dacite pushed up in another area. About 27,000 years ago, Lassen Peak rose from Earth.

The formation of Lassen Peak was not the end of volcanic activity in the park. Small eruptions, lava flow, and even an avalanche or two continued into the twentieth century. Then on May 19, 1915, a huge mass of lava boiled out of the peak. Two days later, an explosion blew a new crater into Lassen Peak. Activity tapered off around 1921, and since then, Lassen Peak has been dormant.

If you ever have the chance to visit Lassen Volcanic National Park, think about the violent, earth-moving history that created the peaceful, pretty park that is there today.

Vocabulary

andesite:

A gray, fine-grained volcanic rock.

basalt:

A hard, dense, dark volcanic rock.

dacite:

A light gray volcanic rock.

dormant:

Not active for a time.

rhyolite:

A fine-grained extrusive volcanic rock, similar to granite in composition and usually exhibiting flow lines.

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Sources:

Lassen Volcanic National Park

http://www.nps.gov/lavo/index.htm

National Audubon Society Field Guide to California.

Peter Alden, editor. Chanticleer Press: New York. 1998. p. 409.