VOLCANIC HAZARDS ASSESSMENT

Human-based Data Sources

Geochemical Data

Geophysical Data

ACTIVE vs. EXTINCT VOLCANOES

• Historians say:• Active volcanoes are those that are erupting

or showing some activity now.• Volcanoes that have erupted historically,

but are inactive at present, are Dormant.• Volcanoes that have had no activity in

historical or archaeological time are Extinct.

ACTIVE vs. EXTINCT VOLCANOES

• To geologists:

• Active volcanoes have magma chambers

• Extinct volcanoes have no magma left in chambers

HUMAN-BASED DATA

• Historical Records• Archaeology• Oral Tradition

• These can help extend the record back to a few thousand years

GEOCHEMICAL DATA

• Radiometric Dates on Volcanic Materials-

– Can extend dates back to millions of years– Give date of last eruption– Give repeat interval of past events– Show which types of volcanic products are

expected

Geophysical Data are used to assess Present-day Risk

• Is Magma Present? Determined by S-wave activity• Heat Flow, especially if increasing• Earthquake Patterns -shallow concentric patterns• Tilting or Bulge of Surface from GPS Data,

Surveying, SAR Interferometry

Earthquakes in Hawaii

EarthquakesIn Iceland

Interferometry: Layering two Images

of separate times on top of one another

to measure vertical change

Top: visual spectrum shows nothing new

Bottom: Interferogram measures areasof differential change due to groundswelling upward. Maximum displacementis in center and pattern is concentric,suggesting a pending volcanic eruption

VOLCANOES IN THE USThere are 33 active volcanoes in the US

Most are at convergent plate boundaries in Alaska and N. California, Oregon, and Washington. These are all stratovolcanoes, which are the most dangerous in terms of explosive activity.

Some are on or near hotspots: Hawaii’s volcanoes, and Yellowstone

Some are former CPB: Central and Southern California

The remainder are on a failed rift (former divergent plate boundary): Arizona, New Mexico

VOLCANIC HAZARDS• Lava flows• Pyroclastics• Gases

– Heated air– Toxic components– Climate change

• Lahars• Tsunamis• Earthquakes

Volcanic Gases: 80% H2O, plus CO2, SO2, and also CO,

H2S

GLOBAL COOLING DUE TO LARGE ERUPTIONAsh injected into Stratosphere circulatesaround the world for up to 3 years

Lahar floods Armero, Colombiaafter eruption of Nevado del Ruiz

Krakatau, 1883

Lava and slope collapse produced a tsunami up to 40m high.

-Killed 36,000 people in SE Asia

-Effects of Tsunami felt 7000 miles away

Ash and gases produced global cooling that lasted 3 years