St. Augustine Volcano Essay, Research Paper
St. Augustine Volcano
Augustine Volcano is the most often active and the youngest of the Cook Inlet vents. Detterman considered Augustine to be wholly Quaternate and Johnston concluded that volcanism at Augustine began during the late Pleistocene Moosehorn glacial progress 19,000-15,500 IBP. Since its find by Captain James Cook in 1778, Augustine Volcano has had seven historical eruptions. 1883, 1935, 1979, 1985, 1986, and 1987. Yount and others, 1987. The activity in 1908, reported by the captain of a steamer enroute to Seward, was minor and likely did non bring forth any sedimentations.
The 1883 eruption appears to hold been the most violent historical eruption of Augustine, and is thought to hold generated a tsunami with wave highs of 7.5 to 9 m at English Bay on the Kenai Peninsula 80 km E of the Davidson Islands, 1884. The tsunami has been attributed to a debris avalanche from the north side of the vent into Cook Inlet.
The most recent eruption, which began on March 27, 1986, after more than five hebdomads of increased seismal activity and continued through August 1986 and, is likely typical of most Augustine eruptions. A about uninterrupted ash-rich plume rose 3,000 to 4,600 m ; periodic explosive explosions reached heights of 12,200 m. Numerous pyroclastic flows were generated in the early phases of the eruption and moved down the north wing. Several big flows reached the north shore 5 kilometer off and entered the sea. Much of the snowpack on the upper wings melted bring forthing lahars. As the eruption evolved, coevals of pyroclastic flows diminished and dome edifice began. A short lava flow besides issued down a steep gully on the north wing.
Military and commercial air traffic was disrupted in upper Cook Inlet during the first hebdomad of the eruption when airborne ash
was traveling northerly. Light ashfall occurred over most of the Cook Inlet country, and ash was detected as far north as the Brooks Range several yearss into the eruption.
Volcanic eruptions of Augustine typically consist of multiple stages crossing several months. During each stage, mudflows and pyroclastic flows frequently accompany explosive ash eruptions. Normally the first stage is the most violently explosive ; consecutive stages frequently include bulge of lava, enlarging the cardinal dome and lava flow composite.
Augustine volcanic stones are of calc-alkaline landsite and deceit composing but of the low-K, instead than medium-K assortment. Phenocryst phases include plagioclase the dominant stage, orthopyroxene, clinopyroxene, hornblende, and rare olivine. Much of the lava is rich in glass and extremely vesicular. Jurassic and Cretaceous sedimentary strata form a bench on the south side of the island and are overlain by granitoid glacial erratics and hyaloclastites. The vent consists of a cardinal dome and lava flow composite, surrounded by pyroclastic dust. The irregular coastline of Augustine Island is due to the repeated ruinous prostration of the acme dome, organizing dust avalanches down the wings and into Cook Inlet. At least 11 avalanches have occurred in the past 2000 old ages with an mean return interval of about 150-200 old ages. Augustine lies within the country of uplift ensuing from the 1964 Alaska temblor ; 30-33 centimeter of upheaval was measured on the northwest Augustine Island, an 8 by 11 kilometers island in lower Cook Inlet is composed about wholly of the side of the island. A 25-meter-high, south-facing pigboat scarp 3 kilometer South of the island, of similar orientation to joint sets in sedimentary stones of the Kamishak River country on the Alaska Peninsula, is about surely of tectonic beginning. There are no people that live on the island, it is a island with a vent on it.