Archived Updates

Anatahan Volcano Update for September 15
Submitted Tuesday, September 16, 10:00 a.m. local Anatahan time

Anatahan volcanic seismicity has remained low, at levels similar to those since June. There were no apparent eruption signals or precursory events.

Several small-amplitude, long-period events are visible on records from the recently re-installed Anatahan station (ANAT) on the southwest rim of the caldera. These events appear to have a predominant frequency of 4-5 Hz, lasting up to 15 seconds. Many of the larger events have a short burst of higher frequency (6-7 Hz) energy about 2.5 seconds after the event onset. The largest of the events occurred at 1233, 1701, 1709, 1851, and 1912 UTC. They are barely above background at the eastern Anatahan station (ANA2) and may have been occurring for the past several weeks undetected. ANAT seems to be considerably more sensitive than ANA2.

Note: the following was modified on September 16, HST. Two regional events were detected by the seismic net. The first, occurring at 0705 UTC, was probably located south of Saipan at a slant distance of about 120 km (or 260 km south of Anatahan). The second at 2330 UTC was located at a slant distance of about 150 km (90 miles) from Anatahan, possibly beneath the Marianas trench.

Anatahan Volcano Update for September 16
Submitted Wednesday, September 17, 10:00 a.m. local Anatahan time

Anatahan volcanic seismicity has remained low, at levels similar to those since June. There were no apparent eruption signals or precursory events. The Earthworm acquisition system was not working from about 0808 UTC to 1825 UTC and 2311 to 2320 UTC due to system problems. Several of the small LP events described yesterday were recorded on the ANAT station.

Two small regionals were recorded by the network, at 1052 and 1147 UTC. The first was at a slant distance of about 260 km south of Anatahan; the second was considerably further away.

Anatahan Volcano Update for September 17
Submitted Thursday, September 18, 10:00 a.m. local Anatahan time

Anatahan volcanic seismicity has remained low, at levels similar to those since June. There were no apparent eruption signals or precursory events. Due to system diagnostics and repair, the Earthworm acquisition was sporadic between 0044 and 0152 UTC and between 1516 and 1612 UTC. Several of the very small LP events seen almost exclusively on ANAT continue to occur, at a rate of 1-3 per hour.

No significant regional activity was recorded by the seismic network. However, a core phase (PKP) from a M6 event near the Chile-Bolivia border was well-recorded at 2154 UTC on all four stations.

Anatahan Volcano Update for September 18
Submitted Friday, September 19, 10:00 a.m. local Anatahan time

Anatahan volcanic seismicity has remained low, at levels similar to those since June. There were no apparent eruption signals or precursory events. Several of the very small LP events seen almost exclusively on ANAT continue to occur at a rate of several per hour. A small event at 1956 UTC with an S-P interval of just under 2 seconds at ANAT appeared to be of the shallow volcano-tectonic variety, with a predominant frequency in the 8-10 Hz range. It was not visible on the ANA2 (east Anatahan) record.

Two regional events were recorded. The first occured at 1259 UTC, appearing shallow and to the south of Anatahan. The second occurred at 1342 UTC at a slant distance of about 100 km from Anatahan, again coming from the south of the island.

On September 18, USGS and EMO personnel took an overflight of Anatahan. There were no ash emissions. The plume from the crater, as before, consisted of steam and sulfur dioxide gas. The floor of the crater appears to be covered by muddy water instead of the shallow lake observed last week. The muddy crater floor remains active, characterized by boiling mud pots, mini-geysers (occasionally hurling small black ejecta), and steam jetting from the crater walls around the water edge.

Anatahan Volcano Update for September 19
Submitted Saturday, September 20 at 10:00 a.m. local Anatahan time

Anatahan volcanic seismicity has remained low, at levels similar to those since June. There were no apparent eruption signals or precursory events.

A regional event was recorded by the seismic net at 1253 UTC, at a slant distance of about 100 km from both Anatahan and Saipan.

Anatahan Volcano Update for September 20
Submitted Sunday, September 21 at 10:00 a.m. local Anatahan time

Anatahan volcanic seismicity is low, at a level similar to that since June. There were no apparent eruption signals or precursory events.

A magnitude 5.2 event located about 80 km south-southeast of Tokyo, Japan, at a depth of 52 km (USGS/National Earthquake Information Center) was recorded by the Sarigan and both Anatahan stations just after 0359 UTC. No significant regional activity occurred during the past 24 hours.

Anatahan Volcano Update for September 21
Submitted Monday, September 22 at 10:00 a.m. local Anatahan time

For the past 24 hours, Anatahan volcanic seismicity has been low, at a level similar to that for the last month of so. There were no apparent eruption signals or precursory events. Tremor and seismic energy release are low.

Contact persons:
Juan Takai Camacho, Geophysical Seismic Technician, EMO Saipan; tel: (670) 322-9528, fax: (670) 322-7743, email: juantcamacho@hotmail.com
Ramon Chong, Geophysical Instrument Specialist, EMO Saipan; tel: (670) 322-9528, fax: (670) 322-7743, email: rcchongemo@hotmail.com
Frank Trusdell, Geologist, USGS; tel: (808) 967-8812, fax: (808) 967-8890, email: trusdell@usgs.gov