Predicting volcanic eruptions

F D C B A

Outline • Review of igneous rocks, magmas, and types of volcanoes • Peaceful vs. explosive eruptions • Predicting volcanic eruptions • Airplane flight paths and risks posed by volcanic ash

Texture Chemical Composition Plutonic Volcanic

Plutonic & volcanic equivalents Felsic Rhyolite Granite Obsidian Quartz monzonite Andesite Gabbro Basalt Mafic Plutonic Volcanic

2) Dissolved gases in the magma What controls whether an eruption is a peaceful lava flow or explosive? SiO2 Viscosity of the magma SiO2 — Composition (How much SiO2?) — Temperature 2) Dissolved gases in the magma Dissolved gases

Magmas vs. Eruptions Peaceful… Explosive! Mafic Felsic SiO2 Temperature (1000-1200°C) (800-1000°C) Viscosity

Low SiO2 magmas = Low gas content = Shield volcanoes High-SiO2 magmas = High gas content = Composite volcanoes

Explosivity of volcanoes VEI Description Plume Height Volume How often Example 0 non-explosive 100 m 1000s m3 daily Kilauea 1 gentle 100-1000 m 10,000s m3 daily Stromboli 2 explosive 1-5 km 1,000,000s m3 weekly Galeras, 1992 3 severe 3-15 km 10,000,000s m3 yearly Ruiz, 1985 4 cataclysmic 10-25 km 100,000,000s m3 10's of years Galunggung, 1982 5 paroxysmal 25 km 1 km3 100's of years St. Helens, 1980 6 colossal 25 km 10s km3 100's of years Krakatau, 1883 7 super-colossal 25 km 100s km3 1000's of years Tambora, 1815 8 mega-colossal 25 km 1,000s km3 10,000's of years Yellowstone, 2 Ma

Haleakala, Maui Shield volcano

Peaceful eruption

Composite volcanoes — think subduction!

Volcanism around the globe

The Tectonic Plates

Mount St. Helens — Before Composite volcano

Explosive volcanism Mount St. Helens — May 18, 1980

Mount St. Helens — After

Predicting eruptions Before an eruption, magma moves into the area beneath the volcano and collects in a magma chamber; this magma movement causes changes in the volcano that scientists can measure.

Predicting eruptions 1. Gas released - Measure volume and composition 2. Small earthquakes produced Measure with seismometer, look for harmonic tremors 3. Slight swelling of the volcano slope. Measure with tiltmeter, GPS 4. Hydrologic changes

Seismicity at Mount St. Helens in 1980

Seismicity at Mt. St. Helens in the last 10 years

Seismicity and depths of seismicity Mount St Seismicity and depths of seismicity Mount St. Helens in the last 10 years

Notice how big these earthquakes are...

How is seismicity before a volcanic eruption different from seismicity related to subduction zones?

How is seismicity before a volcanic eruption different from seismicity related to subduction zones? They differ in the… • Size (magnitude) of the earthquakes • Location of the hypocenters • Types of seismic waves generated • Cause of the quakes

Regular, constant shaking related to Harmonic tremors Examples from Mt. St. Helens Regular, constant shaking related to magma moving underneath a volcano

Harmonic tremors vs. P- and S-waves

New lava dome Mount St. Helens February 25, 2005

Mt. Rainier

Mt. Ranier The periodic melting of glacier ice from Mt Mt. Ranier The periodic melting of glacier ice from Mt. Rainier has generated at least 50 major lahars over the past 10,000 years. A major mudflow descends down the White River once every 600 years. More than 300,000 people now live in the area covered by these extensive lahars!

Lahar or mud flow — One of the deadliest hazards that occur with snow melt or rain

Mayon volcano, Philippines Ash — Most common type of eruption Pyroclastic flows — One of the deadliest hazards

Mt. Pinatubo — the Philippines — June 1991

Clark Air Force base before and after — The Philippines 1991