Form and structure

Mount Trident is an eroded volcanic complex consisting of numerous domes (up to 23), as high as 1864 m in elevation, along a northeast-southwest oriented volcanic front on the Pacific Ocean side of the Alaska Peninsula. A new dome was emplaced beginning in 1953 at an altitude of 1097 m in an amphitheater on the southwest flank of the southwest peak.

Volcanic activity 1953-1960

There is no evidence of recent eruptive activity at the summit of Trident, nor have there been any reports of historical activity, except fumarolic activity on the east side. However, a satellite cone formed February 15, 1953 on the southwest flank of Mt. Trident following a major explosive eruption that sent ash to an altitude of over 9 km. A succession of blocky lava flows were erupted in 1954, 1957, 1958, 1959-1960 from the new vent. Ash eruptions, some to altitudes over 12 km, were associated with several of the lava eruptions. By 1960 the dome had grown nearly 260 m high and a sequence of viscous flows, up to 300 m thick and covering an area of 5 km² south of the volcano, had been extruded. In 1983, steam and/or vapor continued to rise from the central vent area of the new cone as well as from numerous fumaroles on the near-vent portion of the blocky lava flows.

Composition

Trident lavas are andesitic to dacitic in composition. The dominant phenocrysts are zoned plagioclase, hypersthene, calcic clinopyroxene, titanomagnetite, and rimmed olivine. The five flows erupted from the new vent during 1953-1963 are olivine-bearing, two pyroxene, high-silica andesite.