Introduction
Mt. Erebus, Ross Island, Antarctica, is currently the most active volcano in Antarctica. The summit of Mt. Erebus contains a persistent convecting lava lake which undergoes several strombolian style eruptions daily. Within the past year, small ash eruptions and even a small lava flow have also been observed coming from vents near the lava lake.
Mt. Erebus (3794 meters above sea level) is classified as a polygenetic stratovolcano. The composition of the current eruptive activity on Mt. Erebus is anorthoclase-phyric tephriphonolite and phonolite, which constitute the bulk of exposed lava flow on the volcano. The oldest eruptive products from Mt. Erebus consist of relatively undifferentiated and non-viscous basanitic lavas that form the low, broad platform shield of the Erebus edifice. Slightly younger basanites 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 the Mt. Erebus edifice.
Lava flows of more viscous phonotephrite, tephriphonolite and trachyte are erupted after the basanites. The upper slopes of Mt. Erebus are dominated by steeply dipping (~30°) tephriphonolite lava flows with large scale flow levees. A conspicuous break in slope at approximately 3200 meters is a summit plateau representing a caldera. The summit caldera itself is filled with small volume tephriphonolite and phonolite lava flows. In the center of the of the summit caldera is a small, steep-sided cone composed primarily of decomposed lava bombs and a lag deposit of anorthoclase crystals. It is within this summit cone that the active lava lake continuously degasses and periodically erupts.
CAVEAT: Despite the database of information on the geology of Mt. Erebus, there is still much to be learned about the volcano. The relative lack of knowledge becomes apparent when Mt. Erebus is stacked up against other active volcanoes of the world. There are many reasons for this comparative lack of knowledge, including the scarcity of rock exposures due to snow and ice cover, the remoteness of the volcano, the extreme environment, the brief field season (<6 weeks per year) and its non-threatening nature (i.e. no large populations are in jeopardy because of Mt. Erebus, unlike Vesuvius in Italy or Popocatepetl in Mexico).
Despite the above factors limiting the Mt. Erebus knowledge base, clearly much has been learned about the volcano over the past 25+ years. Nearly all exposed lava flow sets on Mt. Erebus have been physically sampled. Nearly all of these have been examined petrographically and petrologically. The summit lava flows on Mt. Erebus have been extensively mapped and dated by the 40Ar/39Ar method. The flank flows have been mapped in less detail, but many have also been dated. Tephra from Mt. Erebus has been found in glaciers on the volcano, mapped, geochemically examined and dated. The morphological characteristics of the edifice have been combined with the geochronological data to provide an evolutionary history of Mt. Erebus. And the physical and eruptive characteristics of the summit lava lake has been observed nearly every year for the past 25 years.
The following pages will hopefully provide you with an idea of the science that has been conducted at Mt. Erebus.