Volcanology 101

There is so much ancient volcanic evidence in Washington, Oregon, and Northern Cal, veteran hikers soon learn the terms used by scientists to describe peaks, rocks, mounds, and soil strata; that is, if you want to sound like a highly astute, primal "old hand", you use the geologists' vocabulary.

A favorite spot for many NW backpackers in Oregon is Mt. Jefferson. The mountain itself tops out at 10,000+ feet and is cloaked with five glaciers. The land surrounding it is primitive, unspoiled, and isolated. Hopefully, it will stay that way since all 111,000+ acres are managed by the National Forest Service and are designated partly as a National Park and partly a "wilderness" area. Those familiar with the Pacific Crest Trail know it passes through an area called Jefferson Park. This so-called "park" lies in the center of the Jefferson Wilderness and is backpacker heaven with dozens of cold, clear lakes.

However, the main attraction is Mt. Jefferson, an extinct (we hope!) volcano, that reaches 10,497 ft. in height. If you are really into volcanoes, you'll love the geology of Jefferson Park.

Glossary (Courtesy of USGS)

If you're not familiar with volcanologists lingo, here are some basic definitions you can toss around at cocktail parties:

Ash: Fragments of less than 2 millimeters in diameter of lava or rock blasted into the air by volcanic explosions.

Basalt: Volcanic rock caused by partial melting of the Earth's crust.

Caldera: A large volcanic depression, commonly circular or elliptical when seen from above, caused by a volcano collapsing into itself.

Cinder Cone: A circular or oval cone made up of small fragments of lava from a single vent that have been blown into the air, cooled and fallen around the vent.

Composite Volcano: A steep-sided volcano composed of many layers of volcanic rocks, usually made from high-viscosity (thick like honey) lava, ash and rock debris (broken pieces).

Dome: A steep-sided mound that forms when viscous (thick like honey) lava piles up near a volcanic vent (opening at the surface).

Fumarole: A vent that releases volcanic gases and steam.

Lahar: A mixture of water and rock debris that forms on the slopes of a volcano. Also known as a mudflow or debris flow. The term comes from Indonesia.

Pumice: A light-colored volcanic rock containing lots of bubbles from trapped gases. This rock can sometimes float on water.

Pyroclastic Flow: A hot, fast moving and high-density (thick like a dust storm) mixture of ash, pumice, rock fragments and gas formed during explosive eruptions.

Shield Volcano: A volcano shaped like a bowl in the middle with long gentle slopes made by basaltic lava flows.

Vent: An opening at the surface where magma, gas and steam erupt.

Volcano: A vent at the surface where magma, gas and steam erupt. Also, the landform constructed by volcanic material.

Future Explorations

In the near future, I'm heading back to the Jefferson Wilderness to find - and hopefully photograph - some of the glaciers and maybe a vent or two. Since the Wilderness is located at an elevation of 7,000+ feet, and the trailhead starts at 3,000 feet, I plan on a slow, leisurely hike into the park, with plenty of time for campsite locating, fishing, and exploration.

Part of the advance planning includes determining and loading at least 20-30 waypoints into my GPS for a four-day trip. I don't know which is the most fun - the planning or the execution. Decisions, decisions!