|
Mount Erebus is the second highest volcano in Antarctica (after Mount Sidley) and the southernmost active volcano on earth. It is the sixth highest ultra mountain on an island.〔 〕 With a summit elevation of , it is located on Ross Island, which is also home to three inactive volcanoes, Mount Terror, Mount Bird, and Mount Terra Nova. The volcano has been observed to be continuously active since 1972 and is the site of the Mount Erebus Volcano Observatory run by the New Mexico Institute of Mining and Technology.〔 (【引用サイトリンク】 Mount Erebus Volcano Observatory )〕 ==Geology and volcanology== Mount Erebus is currently the most active volcano in Antarctica and is the current eruptive zone of the Erebus hotspot. The summit contains a persistent convecting phonolitic lava lake, one of five long-lasting lava lakes on Earth. Characteristic eruptive activity consists of Strombolian eruptions from the lava lake or from one of several subsidiary vents, all within the volcano's inner crater. The volcano is scientifically remarkable in that its relatively low-level and unusually persistent eruptive activity enables long-term volcanological study of a Strombolian eruptive system very close (hundreds of metres) to the active vents, a characteristic shared with only a few volcanos on Earth, such as Stromboli in Italy. Scientific study of the volcano is also facilitated by their proximity to McMurdo Station (U.S.) and Scott Base (N.Z.), both sited on Ross Island approximately thirty-five kilometres away. Mount Erebus is classified as a polygenetic stratovolcano. The bottom half of the volcano is a shield and the top half is a stratocone (Mount Etna is like this as well). The composition of the current eruptive products of Erebus is anorthoclase-porphyritic tephritic phonolite and phonolite, which are the bulk of exposed lava flow on the volcano. The oldest eruptive products consist of relatively undifferentiated and non-viscous basanite lavas that form the low broad platform shield of Erebus. Slightly younger basanite and phonotephrite lavas crop out on Fang Ridge—an eroded remnant of an early Erebus volcano—and at other isolated locations on the flanks of Erebus. Erebus is the world's only presently erupting phonolite volcano. Lava flows of more viscous phonotephrite and trachyte erupted after the basanite. The upper slopes of Mount Erebus are dominated by steeply dipping (~30°) tephritic phonolite lava flows with large scale flow levees. A conspicuous break in slope at approximately 3,200 metres calls attention to a summit plateau representing a caldera less than one hundred millennia old. The summit caldera itself is filled with small volume tephritic phonolite and phonolite lava flows. In the center of the summit caldera is a small steep-sided cone composed primarily of decomposed lava bombs and a large deposit of anorthoclase crystals known as Erebus Crystals. The active lava lake in this summit cone undergoes continuous degassing. Researchers spent more than three months during the 2007–08 field season installing an unusually dense array of seismometers around Mount Erebus to listen to waves of energy generated by small, controlled blasts from explosives they buried along its flanks and perimeter and to record scattered seismic signals generated by lava lake eruptions and local ice quakes. By studying the refracted and scattered seismic waves, the scientists produced an image of the uppermost (top few km) of the volcano to understand the geometry of its "plumbing" and how the magma rises to the lava lake. 〔(【引用サイトリンク】work= )〕 These results demonstrated a complex upper-volcano conduit system with appreciable upper-volcano magma storage to the northwest of the lava lake at depths hundreds of meters below the surface. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mount Erebus」の詳細全文を読む スポンサード リンク
|