The Elliptical Agrihan Island

Agrihan Island

At that special time of day in the hour before sunset, the 3,166-foot peaks of the tallest volcanic mountain in the Marianas is lit up in a warm glow. The giant caldera is best visited by helicopter. Huge tree ferns and tall grasses grow inside. Circle the island and you'll see small pocket beaches and a jagged coast where lava once flowed into the ocean. The wide black sand beach on the south side may be wide enough to land a plane in an emergency. This place, near the inhabited village, is as good a place as any to camp.

Clouds drape the flat-topped summit of Agrigan, the highest of the Marianas arc volcanoes, in this view from the south. The elliptical island is 8 km long; its 965-m-high summit is the top of a massive 4000-m-high submarine volcano, the second largest in the Mariana Islands. An elongated summit caldera is 1 x 2 km wide, 500 m deep, and is breached to the NW. The vegetated flanks of the volcano consist almost entirely of pyroclastic deposits that are more than 100 m thick on the SW flank. The highest of the Marianas arc volcanoes, Agrigan contains a 500-m-deep, flat-floored caldera.

The elliptical island is 8 km long; its 965-m-high summit is the top of a massive 4000-m-high submarine volcano, the second largest in the Marianas Islands. Deep radial valley 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 volcano's 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.

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