Lecture 6:

Tsunamis

Our Hazardous Environment

GEOG 1110Dr. Thieme

Tsunami

• Japanese for "large harbor wave"• catastrophic impacts occur thousands of

kilometers from geologic source• Four possible causes

– earthquake (along subduction zone)– underwater landslide– collapse of a volcano– asteroid impact

Subduction Zone

Indonesian Tsunami

• Indian and Australian plates

• eastward subduction beneath Eurasian plate

• "stick-slip" of subducting plates

• M 9.1 Earthquake on December 26, 2004

Banda Aceh

• provincial capital on northern

Sumatra• shaking by

earthquake• pummeling waves• flooding after land

subsided

Distant vs. Local

• water depth varies as wave

departs epicenter•wave splits into• "local" tsunami

along adjacent coast

• "distant" tsunami in deep

water

Local Tsunami

• 1993 in Sea of Japan

• 15-30 m waves struck Okushiri

Island• arrived only 2-5

minutes after earthquake

• 120 people killed

Tsunami Warning System

• "buoys in the ocean"

• depth gauges

• water pressure recorder on sea bottom

• also need PUBLIC EDUCATION ! !

Tsunami Runup Map

Tsunami Hazard Map

• indicates possible areas of wave impact

• based upon elevation

• slope of sea bottom

• orientation of coast