There are nine active volcanoes in Northern California
The Cascades Mountain Range in Western North America begins in the northern portion of the state of California and extends northward through Oregon and Washington, and into British Columbia. There are 10 major active volcanoes found in this range, all in the United States. Of those, three are in Northern California.
Besides the three Cascades volcanoes, Northern California according to USGS has six more active volcanoes, only one of which they rate at high probability for a future eruption. The others are ranked low to very low. The one ranked high is called the Clear Lake Volcanic Field.
Below I discuss the three major Cascades peaks individually, and also Clear Lake Volcanic Field. I then give summaries of the other five active volcanoes found in Northern California, which are ranked by USGS as having a low to very low threat of a future eruption.
Active volcanoes are often defined as having erupted within the past 10,000 years and likely to erupt again someday. For more about basic volcanology terms, see my InfoBarrel article, Types of Volcanoes and Basic Volcanology Terms.
Latest eruption was in 1915
Lassen Peak is a stratovolcano located in Northern California, and it is the southernmost of the volcanoes that are part of the Cascade Mountain Range.
The most recent eruption occurred in 1915, during World War I. The volcano stands prominently above the surrounding terrain, and peak elevation is 10,462 feet (3,189 meters). Along with Mount St. Helens in the state of Washington, this is one of two volcanoes that erupted in the continental United States during the 20th century.
When Lassen Peak’s latest eruption occurred, it was the first activity known for the volcano since 27,000 years ago. This is an example of why the 10,000 years rule doesn’t necessarily mean a volcano won’t become active again if more than that amount of time has passed.
The volcano and surrounding area comprise Lassen Volcanic National Park. The park is located in Shasta County, along State Route 89. It has many fascinating volcanic features such as cinder cones, lava pinnacles, craters, sulfur vents, and hot springs.
Lassen Park is a stratovolcano, although after the 1915 eruption it built up a massive lava dome, which I have seen several sources call the largest lava dome on Earth.
Video of beautiful Lassen Volcanic National Park
Medicine Lake Volcano
Latest eruption was 900 to 1,000 years ago
Medicine Lake Volcano is a shield volcano found in northern California, almost at the border with Oregon, and about 30 miles (48 km) northeast of Mount Shasta (discussed next below). The latest eruption occurred about 900 to 1,000 years ago. By comparison, in 1025 AD the Byzantine Empire was at its peak.
The volcano stands high above the surrounding region, and the peak elevation is 7,921 feet (2,414 meters). It is the largest volcano, by volume, in the Cascade Mountain Range. The northeastern flank of the volcano is the site of Lava Beds National Monument, famous for its lava tube caves and other volcanic features, plus Native American rock art and excellent hiking trails.
Medicine Lake itself is about 4.3 by 7.5 miles (6.9 by 12.1 km) in size, and sits in the volcano’s central caldera.
Latest eruption was in 1786
The picture at the top of this article is Mount Shasta. One time I flew on an airplane from San Francisco, California to Medford, Oregon – and seeing this volcano was definitely the highlight of the flight. To call it awesome is an understatement.
Mount Shasta is the largest stratovolcano, by volume, in the Cascade Mountains. This incredible mountain towers more than 9,000 feet (2,700 meters) above the surrounding landscape, with a peak elevation of 14,179 feet (4,319 meters), making it one of the tallest mountains in California, and the second tallest volcano in the Cascades after Washington state’s Mount Rainier.
The most recent eruption occurred in 1786, just a year before the United States Constitution was agreed upon at the Constitutional Convention in Philadelphia. The first that anyone who is not a Native American saw Mount Shasta was in 1826. The mountain has, over the past several thousand years, had a large eruption approximately every 600 years.
The main area for recreation is south and southwest of the mountain, near the town of Mount Shasta. Hiking to the mountain’s summit is common, and although not recommended in the winter, many people still try it.
Clear Lake Volcanic Field
Latest eruption was about 10,000 years ago
By the date of its most recent eruption, estimated to have been around 8,000 BC, this volcano is surpassing the 10,000 year threshold for being called an active volcano. However, USGS rates the threat potential for another eruption as high.
This lava field is located about 90 miles (145 km) north of San Francisco, and the town of Clear Lake, as well as the body of water it is named after, are located within it.
Small earthquakes originating with the volcano occur sporadically. Heat from the volcano is harnessed by a geothermal power plant that produces electricity for 850,000 homes. There are many hot springs in the area as well, also heated by the magma.
Within the volcanic field, the most prominent feature, which is where the most recent eruption took place, is a lava dome called Mount Konocti, standing about 3,200 feet (975 meters) above Clear Lake. The volcano continues to be monitored, and the hot springs and volcanic gases in the region are periodically analyzed.
Five more Northern California volcanoes
All five of these may or may not have erupted within the past 10,000 years. It’s possible that none, some, or all erupted toward the end of the Pleistocene, more than 11,700 years ago – or in could have been more recent.
Each of these five volcanoes is rated by USGS as having a low to very low threat for a future eruption, although none have been declared extinct. If not meeting the criteria for active volcanoes, they are at least dormant with a possibility of future activity.
Located in Shasta County, this is actually a small shield volcano. There are lava flows that have an appearance of being not more than a few thousand years old, although the true age is not yet certain.
Eagle Lake Volcanic Field
This is an area with 15 cinder cones and vents, located in Lassen County at the edge of the Cascades and the Great Basin. The greatest activity at this site took place more than 50,000 years ago, although there is also evidence of activity having taken place during the Holocene (11,700 years ago to the present) as well.
Silver Lake Volcanic Field
This is two cinder cones in Shasta County. The lava flows are responsible for the formation of three small lakes. Their age is not certain, although geologists say that their age is possibly within the Holocene.
A line of cinder cones in Shasta County follows a north-northwest to south-southeast running fissure. Of the lava flows originating here, the most prominent is called Devils Rock Garden. This lava flow, originating from Tumble Butte, is the youngest in the area and is certainly younger than 15,000 years old, although may or may not be as young as 10,000 years.
Also in Shasta County (notice how many great volcanoes there are in Shasta County?), this is a group of cinder cones located southeast of a lava dome called Burney Mountain, which is a Pleistocene-era volcano. The cinder cones are said to possibly be of Holocene age, meaning they may have erupted less than 10,000 years ago.