Beginning about 06:35 24 April ChST (20:35 23 April UTC), seismic stations on Pagan, Sarigan, Anatahan and Saipan began recording signals believed to be from an undersea volcanic source north of Pagan Island. Data from hydroacoustic sensors on Wake Island indicate that the source of this seismic activity is at or near Ahyi seamount. It is not possible to locate the source of the activity precisely and it may be that the unrest is associated with one of the other volcanic seamounts in the area.
The level of seismic activity remains high and has changed little over the past several days. So far, USGS has received no reports of an eruption plume or any evidence that the submarine activity is producing eruptive products that have reached the surface. Satellite images show nothing out of the ordinary.
It is possible, but by no means certain, that the unrest at or near Ahyi seamount will continue to escalate and become a vigorous submarine eruption, possibly associated with an explosive eruption column rising above sea level. If this happens, it is possible for accumulations of pumice and other volcanic debris to form and be visible on the surface of the ocean and in the water column. Local disturbances of the water column may result in violent wave action that may initiate a local tsunami. If a large eruption occurs, it is possible for an eruption column to form and ash fallout may result. It is not possible to predict how high an eruption column from a submarine vent might rise, but eruption clouds reaching 20,000 feet above sea level would not be unusual.
Sudden explosions and accumulations of floating volcanic debris could be hazardous to marine vessels. If an eruption persists for several days, or is particularly voluminous, accumulations of floating volcanic debris may remain in a concentrated state for some time and thus could pose an ongoing hazard to mariners even though eruptive activity has declined or ended. Upwelling of warm, gas-laden water above the eruption site also may occur and this could decrease local water density and thus pose a navigation hazard to ships in the immediate vicinity of the rising water.
The USGS will continue to monitor the unrest closely and will issue additional information as the situation warrants. Mariners are encouraged to remain alert and report any unusual sea conditions or debris in the vicinity of Ahyi seamount to USGS or the CNMI Emergency Management Office using the contact information provided below.
CONTACT INFORMATION:
USGS Northern Marianas Duty Scientist (808) 967-8815
http://volcano.wr.usgs.gov/cnmistatus.php
CNMI Emergency Management Office (670) 322-8001
http://www.cnmihomelandsecurity.gov.mp/
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