An overflight on 1 August revealed increased fumarolic activity at the volcano [(figure 1)]. Nine residents were evacuated from the island. No felt earthquakes were reported.

Figure 1. Geologic map of Agrigan after Stern (1978). Contour interval is 200 m.

Reference. Stern, R.J., 1978, Agrigan: an introduction to the geology of an active volcano in the Northern Mariana Arc: BV, v. 41, p. 43-55.

Geological Summary. The highest of the Marianas arc volcanoes, Agrigan contains a 500-m-deep, flat-floored caldera. The elliptical island is 8 km long; its summit is the top of a massive 4000-m-high submarine volcano. Deep radial valleys dissect the flanks of the thickly vegetated stratovolcano. The elongated caldera is 1 x 2 km wide and is breached to the NW, from where a prominent lava flow extends to the coast and forms a lava delta. The caldera floor is surfaced by fresh-looking lava flows and also contains two cones that may have formed during the only historical eruption in 1917. This eruption deposited large blocks and 3 m of ash and lapilli on a village on the SE coast, prompting its evacuation.

Information Contacts: R. Koyanagi, HVO; F. Sasamoto, Office of Civil Defense, Saipan.