Volcanoes

3 types of volcanoes 9 km 3 km 120-150 km 0.3 km 15 km 1.5 km

Cinder cone volcanoes Smallest, simplest type of volcano (rarely exceeds 400 meters in height) Commonly found on flanks of stratovolcanos, shield volcanoes, or calderas. - Composed of cinders and ash that fall to earth around a volcanic vent following an eruption. Lava ranges from felsic to mafic.

Paricutin Birth and death of a cinder cone volcano Began erupting in Dioniso Pulido’s corn field near Paricutin, Mexico in February 1943. Paricutin, one week old Dioniso Pulido

Paricutin erupting at night Paricutin, 8 weeks old Paricutin is a classic cinder cone volcano Note the lava flowing out San Juan Parangaricutiro Church Paricutin erupting at night

Paricutin erupted from 1943 to 1952. It is now considered extinct. Paricutin erupting in 1943 Paricutin erupted from 1943 to 1952. It is now considered extinct. Paricutin today San Juan Parangaricutiro Church

Shield volcanoes - Large volcanoes with broad, gentle slopes - Formed by basaltic lava flows of low viscosity “aa” lava flow in Hawaii Magma Chamber

Cinder cone formed on Kilauea’s flank

Composite or Stratovolcanoes Very large, tall conical shaped volcanoes Formed by alternating layers of hardened lava and ash Lava is generally felsic and very viscous Very explosive and dangerous volcanoes

Anatomy of a Stratovolcano Mt. Mayon, Philippines

Mt. Rainier

The Eruption of Mount St. Helens May 18, 1980

The View from Johnston Ridge – One day before the eruption Elevation 9,677 feet

The View from Johnston Ridge – Shortly after the eruption Elevation 8,364 feet

The View from Johnston Ridge – Four years after the eruption Dome beginning to fill crater Drainage channels developing

David A. Johnston December 1949 - May 18, 1980 So, why is it called Johnston Ridge? David A. Johnston December 1949 - May 18, 1980 David Johnston at Coldwater II, at 1900 hours. Dave did not survive the next day's eruption. Coldwater II would eventually be re-named "Johnston Ridge" in honor of Dave. USGS Photograph taken on May 17, 1980, by Harry Glicken.

The Eruption May 18, 1980

The Effects

The eruption blew the top off of the mountain… Helicopter and Human

…caused significant damage to personal property… Damage cause by “lahars” – volcanic mud flows

…as well as the surrounding areas. Before Spirit Lake After

Before Mount Rainier Spirit Lake This view north from the summit of Mount St. Helens shows the pristine forest that surrounded Spirit Lake (lower right) at the base of the volcano before the 1980 eruption. The snow-covered area above Spirit Lake is the Mt. Margaret back country; Mount Rainier looms in the distance.

After October 4, 1980 Mount Rainier Denuded hillslopes from lateral blast Spirit Lake (with downed trees) Approximate site of Harry Truman’s lodge X Pumice Plain October 4, 1980

Another view changed forever… Before Obscurity Lake After

Trees were flattened by the blast, some blown into toothpick-sized splinters. Geologists! The slopes of Smith Creek valley, east of Mount St. Helens, show trees blown down by the May 18, 1980 lateral blast. Two U.S. Geological Survey scientists (lower right) give scale. The direction of the blast, shown here from left to right, is apparent in the alignment of the downed trees. Over four billion board feet of usable timber, enough to build 150,000 homes, was damaged or destroyed.

Other areas felt the effect of massive lahars… Gray mud on trees along the Muddy River marks the height of the lahar as it swept down the river more than 15 km from the volcano. Note person in yellow jacket for scale. Although the lahar reached a depth of at least 10 m in this area, the resulting deposit is less than 1 m on the river terrace where the person is standing.

Aerial view of highway bridge abutments (structures on both sides of the river channel) that once supported a bridge across the Muddy River. The lahar destroyed the bridge and swept over the highway, leaving behind tree trunks and rock deposits that included large boulders (note rocks to right of the highway). Cars This view upstream from the site of the Muddy River bridge shows the large size of boulders carried by the lahar about 21 km from the volcano. The extremely high proportion of rock debris to water in lahars, often more than 70 to 80 percent sediment by weight, enables these boulders to "float" in the moving mixture of water and rock. The lahar traveled down this stretch of the Muddy River from one side of the valley to the other, and during its peak flow was well above the cars in the distance.

A lahar carries away a bridge spanning the Toutle River about 55 km downstream from Mount St. Helens volcano on May 18, 1980. Before arriving at the bridge, the lahar swept through a logging camp and picked up thousands of neatly cut and stacked logs from along the river. This lahar originated from the huge landslide that started the eruption at 8:32 in the morning

Pyroclastic flows were massive… Whitish blocks of pumice cover the surface of this day old pyroclastic flow, erupted on October 22, 1980. Just a few centimeters beneath the surface, however, ash dominates the deposit by filling spaces between smaller pieces of pumice. The darker surface beneath the October pyroclastic flow is the deposit of pyroclastic flows formed on May 18, 1980, during the climactic eruption of Mount St. Helens.

Ash fall was extensive.

Mount St. Helens A changed landscape

The Future?