Tsunami Potential and Response for Augustine Volcano Events

December 21, 2005

 

U.S. Tsunami Warning Centers normally do not monitor volcanoes.  The one exception is when a volcano becomes restless and has the potential for generating a tsunami dangerous to coastal populations.  While the probability of a volcanic eruption triggering a damaging tsunami is low, the possibility does exist and the West Coast/Alaska Tsunami Warning Center (WC/ATWC) in coordination with the USGS is watching the current activity at Mount Augustine closely.  A tsunami resulting from an eruption of Mt. Augustine could cause dangerous flooding of low-lying coastal areas surrounding the Lower Cook Inlet between the Barren Islands to the south and Kalgin Island to the north. 

 

The shallow depths of the upper region of Cook Inlet would cause the tsunami to diminish considerably, making the risk to Anchorage extremely low.

 

Background

Mount Augustine is an island-volcano located in the Cook Inlet approximately 70 miles WSW of Homer, Alaska.  It is one of south-central Alaska’s most active volcanoes erupting most recently in 1976 and 1986.  Since 1812, the volcano is known to have gone through seven eruptive periods.  During an eruption in 1883, a large flank collapse (also known as debris avalanche) occurred on the north side of the volcano.  This collapse triggered a tsunami which was observed at Nanwalek as a surge estimated at 6 meters above normal sea level.  The wave was also recorded by a Kodiak tide gage with a 20 cm peak-to-trough amplitude.  According to USGS studies, these flank collapses occur approximately every 150-200 years.  Pyroclastic flows which enter the sea are another potential mechanism by which volcanic eruptions can trigger tsunamis.  These flows have occurred in the recent Augustine eruptions, but have not triggered tsunamis dangerous to the populated coasts and are not expected to do so in future eruptions due to the distance to communities.

 

Large flank collapses have been observed on other volcanoes in modern times: Bezymianny 1956, Sheveluch 1964, and Mt. St. Helens 1980.  The seismic energy release from each was approximately equivalent to a magnitude 5 earthquake.  These events are our best indication of what may be observed on seismic networks due to a potentially tsunamigenic flank collapse at Mt. Augustine.  During the last two Mt. Augustine eruptions, the largest recorded seismic energy release associated with the eruption was equivalent to a magnitude 3.2 earthquake.

 

The WC/ATWC is currently working with the Alaska Volcano Observatory (AVO) and the University of Alaska, Fairbanks TWEAK Program to develop a run-up recorder that could be installed on Augustine Island to give direct evidence of tsunami generation or flank collapse. 

 

Tsunami Warnings

Since it is unusual for flank collapses to occur in conjunction with Augustine eruptions, tsunami warnings will be issued based on both volcanic activity and seismic energy release.  AVO will raise its level of concern to orange or red prior to any significant level of volcanic activity and it is very unlikely that a flank collapse would occur without previous activity that would lead AVO to raise the color code to orange or red.

 

If a seismic disturbance equivalent to an earthquake of magnitude 4.5 or greater is detected at Mt. Augustine and the AVO color code is orange or red a tsunami warning will be issued for the Lower Cook Inlet region north of the Barren Islands and south of Kalgin Island.  The seismic energy release point must also be shallow for a warning to be issued, as many moderate-sized earthquakes that are not related to volcanic activity are triggered at great depths below Augustine. 

 

  • Warnings are broadcast through standard National Weather Service (NWS) dissemination methods such as the NOAA Weather Radio-All Hazards, the Emergency Managers Weather Information Network, and are forwarded to the Emergency Alert System. 
  • State Emergency Service Agencies receive the message through FEMA’s National Warning System and the NOAA Weather Wire.  The states immediately pass warnings to local jurisdictions.
  • The US Coast Guard relays the message via radio.
  • The warnings are posted on the WC/ATWC and NWS web sites (http://wcatwc.arh.noaa.gov) and are issued through a public e-mail list server.
  • The Kenai Peninsula Borough and Alaska State Troopers will activate procedures to notify emergency officials and the public. 
  • The WC/ATWC will also contact at-risk communities directly so that they may enact procedures to notify residents.

 

Travel Times

Map of approximate travel times (in minutes) for a tsunami generated at Augustine Island.  The red line indicates the area which would be put in a warning if a tsunami warning is issued. 

 

 

Location

Distance (mi)

Travel Time (min)

Average Speed (mph)

Barren Islands

54

47

68

Nanwalek/ English Bay

51

57

54

Homer Spit

70

90

47

Anchor Point

60

79

45

Clam Gulch

90

125

44

Oil Bay Area

15

27

32

 

 

Links

For more information on the 1883 Augustine Volcano eruption and tsunami, visit:

·         WC/ATWC web site: http://wcatwc.arh.noaa.gov/web_tsus/18831006/18831006.htm

 

For more information on Augustine Volcano, visit:

·         USGS - Alaska Volcano Observatory: http://www.avo.alaska.edu/

·         NOAA NWS Anchorage Forecast Office's Augustine Special Coordination Page: http://pafc.arh.noaa.gov/augustine.php

·         Alaska Division of Homeland Security and Emergency Management: http://www.ak-prepared.com/.  Click on "Volcano Mitigation."

·         NOAA's Air Resources Laboratory forecast trajectory maps for Alaska’s volcanoes: http://www.arl.noaa.gov/ready/traj_alaska.html

·         NOAA NWS Alaska Aviation Weather Unit:  http://aawu.arh.noaa.gov/

·         NOAA NWS Center Weather Service Unit: http://cwsu.arh.noaa.gov/

·         Volcanic Ash, What It Is, What It Can Do and How to Prevent Damage:  http://volcanoes.usgs.gov/ash/

·         Specific Health Impacts of Volcanic Ash: http://volcanoes.usgs.gov/ash/health/index.html

·         Volcanic Ash Impacts on Air Quality:  http://www.epa.gov/airnow/volcano-events.html

·         Preliminary Volcano-hazard Assessment for Augustine Volcano, Alaska (USGS Open-File Report):  http://www.avo.alaska.edu/pdfs/augustine_ofr.pdf

·         USGS Preliminary Hazard-Assessment Map for Augustine Volcano:  http://www.avo.alaska.edu/pdfs/augustine_plate.pdf