It is filled with small volume tephritic phonolite and phonolite lava flows. The summit caldera was created by an explosive VEI-6 eruption that occurred 18,000 ± 7,000 years ago. A conspicuous break in slope at approximately 3,200 metres calls attention to a summit plateau representing a caldera. The upper slopes of Mount Erebus are dominated by steeply dipping (~30°) tephritic phonolite lava flows with large scale flow levees. Lava flows of more viscous phonotephrite and trachyte erupted after the basanite. Erebus is the world's only presently erupting phonolite volcano. 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. The oldest eruptive products consist of relatively undifferentiated and non-viscous basanite lavas that form the low broad platform shield of Erebus. 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 bottom half of the volcano is a shield and the top half is a stratocone. Mount Erebus is classified as a polygenetic stratovolcano. Scientific study of the volcano is also facilitated by their proximity to McMurdo Station (U.S.) and Scott Base ( New Zealand), both sited on Ross Island approximately thirty-five kilometres away. 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 volcanoes on Earth, such as Stromboli in Italy. 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 summit contains a persistent convecting phonolitic lava lake, one of five long-lasting lava lakes on Earth. Mount Erebus is currently the most active volcano in Antarctica and is the current eruptive zone of the Erebus hotspot.
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