Geology

Newberry Caldera (Crater) was formed 500,000 to 250,000 years ago when Mt. Newberry collapsed leaving a crater 5 miles across and over 2,800 feet deep. Subsequent eruptions divided the caldera into two lakes, and left a pumice cone between them.

The most recent eruption was 1,300 years ago resulting in the youngest lava flow in the Northwest. Visitors will find evidence of a wider variety of volcanic events in a more compressed area here than anywhere else in the United States, and they are all easily accessible. Cinder cones, lava flows laced with obsidian, Oregon's longest lava tube cavern, and fields of pumice are some of the volcanic features that make this place remarkable.

Obsidian: Obsidian is natural volcanic glass. When lava is especially rich in silica (SiO2), it has a stiff consistency of taffy or cookie dough. When the lava cools fairly rapidly, it hardens to rock before its atoms have time to move about and organize themselves into the symmetrical, closely packed structures of crystals. Native American Indians fashioned knives, arrowheads, and other sharp tools from obsidian. Because obsidian blades are sharper than steel, they cause little scarring; some doctors use them today for delicate operations, such as eye surgery.

Lava Flows: Four lava flows abundant with obsidian exist within the Caldera. The Big Obsidian Flow is one of the geologic wonders of the Pacific Northwest, and at 1300 years old is the most recent volcanic eruption in Oregon. Created when rhyolite lava spilled to the basin floor from a high vent and formed frozen cataracts of black, volcanic glass, the Big Obsidian flow has attracted human visitors for hundreds of years. Today, Forest visitors use the 0.9 mile interpretive trail on the flow to gain firsthand knowledge about the black glass and its history.

Lava Casts: Eruptions along the Northwest Rift Zone leading from Newberry volcano sent Pahoehoe (smooth) lava surging to the earth's surface, spilling through the pine forest. Sap stored in live trees was converted to steam by super-heated lava. Steam then cooled the lava, in turn preventing some trees from being burned up completely. Trees were either turned to ash or transformed to charcoal, depending upon the availability of oxygen. Molds formed when lava flowed around tree trunks, quickly cooling to fashion a hard coating. Where the flow of lava was rapid, molds did not form. When the lava slowly receded as a result of down flow drainage, the hardened molds of burned trees stood high above the lava surface. Later, the charred wood rotted away leaving the lava molds. Roots of these vanished trees still remain 10-15 feet below the lava surface. Radiocarbon dates from these roots and recent work done in flow contact areas place the time of eruptive activity at 6,000 years ago.


The Lava Cast Forest Geologic Area, established in 1942 by the USDA Forest Service, envelopes an area of approximately five square miles. The ecosystem consists of ponderosa and lodgepole pines, white fir, shrubs and grasses. Even before the volcanic activity which produced the Lava Cast forest over 6,000 years ago, this land looked very similar to what you see today. Newberry Volcano, located to the south and east, erupted along a series of fissures on its northwest flank, sending smooth-textured pahoehoe lava onto the surface through many vents located along the fissures. Lava surged through the forest, engulfing everything it encountered.

A one mile interpretive trail gives a first-hand look at Nature's ongoing struggle of reclamation. Walking time is about 45 minutes for most people. Skateboards, bicycles, etc., are not permitted on the trail. For convenience, benches are strategically placed beside the trail. For most of its length, the trail is quite flat. Physically challenged individuals, however, need to be aware of hairpin turns located on ascending and descending slopes toward the end of the trail.

The Newberry area has been inhabited by Native Americans intermittently for the last 13,000 years. Archaeologists hypothesize that early inhabitants used the caldera in much the same way we do today - for hunting and recreation - seasonally. Most important was the collection of high quality obsidian for tools and weapons. Obsidian chippings, as well as finished artifacts, have been found in several digs, marking what were probably seasonal camps. Obsidian from Newberry was traded up and down the Pacific Northwest and had been found as far away a British Colombia in Canada. Stone vessels and sagebrush bark sandal found below layers of ash indicated these early inhabitants were around during the volcanic eruptions.