Volcanic History

In May 1914, Lassen Peak burst into eruption, beginning a 7-year cycle of sporadic volcanic outbursts. The climax of this episode took place in 1915, when the peak blew an enormous mushroom cloud some 7 miles into the stratosphere. The reawakening of this volcano, which began as a vent on a large extinct volcano known as Tehama, profoundly altered the surrounding landscape. The park is a compact laboratory of volcanic phenomena and associated thermal features except true geysers. It is part of a vast geographic unit - a great lava plateau with isolated volcanic peaks - that also encompasses Lava Beds National Monument, California, and Crater Lake National Park, Oregon.

Before the 1980 eruption of Mount Saint Helens in Washington, Lassen Peak was the most recent volcanic outburst in the continuous 48 states. The peak is the southernmost volcano in the Cascade Range, which extends from here to Canada. The western part of the park features great lava pinnacles, huge mountains created by lava flows, jagged craters, and steaming sulphur vents. It is cut by spectacular glaciated canyons and is dotted and threaded by lakes and rushing clear streams. Snowbanks persist year-round and beautiful meadows are spread with wildflowers in spring. The eastern part of the park is a vast lava plateau more than 1 mile above sea level. Here are found small cinder cones - Fairfield Peak, Hat Mountain, and Crater Butte. Forested with pine and fir, this area is studded with small lakes, but it boasts few streams. Warner Valley, marking the southern edge of the Lassen plateau, features hot spring areas - Boiling Springs Lake, Devils Kitchen, and Terminal Geyser. This forested, steep valley also has gorgeous large meadows.

The 1980 eruption of Mount Saint Helens reduced Lassen's superlative status, but it increased the park's significance as an over 70-year laboratory of possible recovery patterns for Mount Saint Helens. The Devastated Area evidences the combined mud flow and gas blast destruction typical of many volcanic eruptions in the Cascades. The Chaos Jumbles area looks similarly destroyed, but for a different reason. An air-cushioned avalanche - one that fell so rapidly en masse that it trapped and compresses air beneath itself - crashed down the Chaos Crags about 300 years ago. The air acted as a lubricant, enabling the avalanche to rush across the valley at more than 100 miles per hour. It pushed 400 feet up the side of Table Mountain, before losing its momentum and surging back down across Manzanita Creek.

Lassen geothermal area - Sulphur works, Bumpass Hell (largest), Little Hot Springs Valley, Boiling Springs Lake, Devils Kitchen, and Terminal Geyser - offer bubbling mud pots, steaming fumaroles, and boiling water. Some of these thermal features are getting hotter. Scientists think that Lassen Volcanic National Park and Mount Shasta are the most likely candidates in the Cascades to join Mount Saint Helens as active volcanoes.

Geology

Lassen Volcanic National Park is but one of the active, dormant, or extinct volcanoes that extend around the Pacific Ocean in a great Ring of Fire. This zone of volcanoes and earthquakes marks the edges of plates that form the Earth's crust. Volcanic and seismic disturbances occur as these great slabs override or grind past each other.

The theory of plate tectonics holds that as the expanding oceanic crust is thrust beneath the continental plate margins, it penetrates deep enough into the Earth to be partly remelted. Pockets of molten rock (magma) results. These become the feeding chambers for volcanoes.

About 600,000 years ago a great Pacific Ring of Fire stratovolcano. Mount Tehama gradually built up here through countless eruptions. Before Lassen Peak was emplaced, Mount Tehama had collapsed, but its caldera was breached and no lake developed as did Crater Lake in Oregon. Mount Tehama's main vent was probably what is now the park's Sulphur Works. Remnants of its caldera flanks are Brokeoff Mountain, Mount Diller, Piolet Pinnacle, and Mount Conrad. Connect these peaks in a circle to envision Mount Tehama's base - more than 11 miles wide.

Lassen Peak began as a volcanic vent on Mount Tehama's northern flank. Considered the world's largest plug dome volcano, it rises 2,000 feet to an elevation of 10,457 feet. The peaks lava came from many veins. Recent geological evidence indicates that Cinder Cone, also a volcano, erupted in the 18th century.

How do landscapes recover from volcanic eruptions? That question, asked anew since Mount Saint Helens erupted in 1980, has been answered for more than 70 years - since Lassen Peak quieted down.

The Devastated Area most visibly illustrates the slow but relentless return of Earth's green mantle of plants, but many areas of the park are important post-volcanism plant succession sites. Both the Devastated Area, denuded by volcanic activity, and the Chaos Jumbles, denuded by an air-cushion avalanche, are recovering directly to conifers without preparation by herbaceous plants.

This fact observed at Lassen corrects earlier theories. Many disturbed areas here are being reforested with young trees that are more varied than the mature forests that once stood on them. The apparent reason is lack of competition during the earlier stages of recovery. In the Chaos Jumbles, competition will eventually crowd out four of the eight conifer species presently recovering the area.

Rocky lands at lower park elevations largely result from geologic disturbances. Such nearly soil free areas can show classic re-vegetation patterns. The Devastated Area is undergoing a successional process of re-vegetation, with herbs, grasses, shrub, and finally, trees retaking the land. Lodgepoles, generally the first trees, give way in time to other pines and firs. Although eruptions occurred during the 18th century at Cinder Cone and Fantastic Lava Beds, these areas show no significant vegetative recovery.

 
 
Copyright © 2006-17 Claud "Sonny" Rouch, all rights reserved. Website by OACYS Technology. Cover photo by Roberts Engineering.