Images

An increase in deformation rates is an indication that magma is slowly entering the dome. In the early 1980s deformation rates often reached 30 feet per hour (10 meters/hour) as magma rose and the dome expanded before extrusion started. During the winter months, the instrument stations often had to be dug out of the snow before measurements could be made.

The U.S. Geological Survey established both periodic and continuous 24-hour monitoring programs at Mount St. Helens to study and predict eruptions. In this slide, geologists used a steel tape to measure the distance across a crack on the crater floor. Widening of cracks was an indication that magma was rising and deforming the area, leading to an eruption.

Lava production from these "2,900-m vents" decreased from less than 100,000 m3 per hour on April 9 to about 20,000 m3 on April 13, which was the last full day of eruption. Active lava flows extended less than 2 km from the vents. Note two geologists for scale in lower right (in green flight suits). Mauna Loa summit in upper left.

Lava production from these "2,900-m vents" began to decrease in late March but declined most rapidly between April 7 and 9 from about 300,000 m3 per hour to less than 100,000 m3 per hour. Photo taken at 9:09 a.m.

Blockage and overflow of main ‘A‘ā lava channel leading from the 2,900-m vents; note helicopter below the blockage. Large, floating debris of solidified lava (called lava boats) and debris from surface crusts sometime congregate at constrictions along the channel, causing blockages of the main channel.

After repeated blockages and overflows of the main lava channel between April 5 and 8, the steady supply of lava to well-developed flow fronts below the 1,850-m level ceased. As the lowest flow fronts stagnated and the rate of eruption from the vents slowed, hazard concerns for Hilo diminished.

Lava flows from the 1984 eruption of Mauna Loa loom above the town of Hilo. Photograph taken near the Hilo airport on April 4.

These are 19 km east of the original outbreak point that began within Moku‘āweoweo caldera about 36 hours earlier.

Pohaku Hanalei cinder-spatter cone (upper left) is located about 3.2 km (2 mi) NE from the north edge of the caldera rim. Eruption rates were as high as 2.9 million m3 per hour during the first 6 hours of the eruption, then diminished to about 0.5 million m3 per hour for the next 12 days.

Aa lava flows erupting from Mauna Loa.

The eruption began at 1:25 a.m., and the glow was visible from much of the island. After about 4:00 a.m., the activity migrated into the upper northeast rift zone (to the right of the glow) and diminished in the summit area.

Plume of steam and volcanic gas rises from fissures erupting on the upper northeast rift zone of Manua Loa Volcano. At about 4:30 p.m., lava erupted from a new fissure about 5 to 7 km further down the rift (to the right). This new fissure became the site of all lava production for the remainder of the eruption.

Harry's Ridge monitoring station, 8 km (5 mi) north of Mount St. Helens' crater.

The May 18, 1980 debris avalanche from Mount St. Helens covered over 24 square miles (62 square kilometers) of the upper Toutle River valley and blocked tributaries of the North Fork Toutle River. New lakes such as Castle Lake (pictured here) and Coldwater Lake were created.

Debris avalanche deposit with hummocky terrain resulting from the May 18, 1980 eruption of Mount St. Helens. View to the east toward Coldwater Lake.

Low fountain, approximately 50 meters high, from Pu'u 'O'o on Hawai'i Island's Kilauea Volcano (viewed from the north). Lava issuing from the breach in the northeast rim of the crater produced an 'a'a flow that extended more than 4 kilometers. Eruption episode 8.

Pu'u 'O'o fountain approximately 100 meters high during eruption episode 8 on Hawai'i Island's Kilauea Volcano. Dark clots of spatter land near the base of the fountain, contributing to the growth of the cone. Less dense cinder, visible in the upper right, is carried downwind of the cone.

Accretionary lava ball comes to rest on the grass after rolling off the top of an 'a'a flow in Royal Gardens subdivision on Hawai'i Island's Kilauea Volcano. Accretionary lava balls form as viscous lava is molded around a core of already-soldified lava.

View at dusk of the young Pu'u 'O'o cinder-and-spatter cone, with fountain 40 meters high, on Hawai'i Island's Kilauea Volcano (episode 5).

By 1987, the dome had replaced only three percent of the volume removed by the May 18, 1980 eruption. If that rate of growth had continued it would have taken over 200 years to rebuild Mount St. Helens to its pre-1980 size. Instead, Mount St. Helens entered a quiet period which continued until 2004.

The April 1983 landslide at Thistle, Utah, created a 200-ft-high (60-m-high) blockage of Spanish Fork canyon that caused disastrous flooding of the Thistle creek and Soldier Creek valleys upstream.  The flooding caused by the landslide required relocation of a major highway and railway.  An emergency spillway and diversion tunnels were constructed to drain