Volcanism

Volcanic activity, which is tied to tectonic processes, has been intermittent through the Antarctic continental history. The late Cenozoic volcanic cycles are responsible for the actual morphological features seen today in parts of the Western Antarctica. The Transantarctic Mountain Range has ten volcanoes of which two are currently active; Mount Erebus and Deception Island

The world’s southernmost historically active volcano, Erebus is the largest of three major volcanoes forming a roughly triangular Ross Island. The summit has been modified by several generations of caldera formation. A summit plateau at about 3000m altitude marks the rim of the youngest volcano. An elliptical 500m x 600mm wide, 110m deep crater truncates the summit and contains an openly convecting phonolitic lava lake within a 250m x100m wide crater.

Erebus has been erupting since its discovery by Capt. James Ross in 1841. Lava lake activity has been documented continuously since 1972, with almost daily Strombolian explosions typically erupting from the lake, sending showers of anorthoclase crystals, glass and bombs upwards, to fall onto the crater rim. In the main the eruptions are limited to within the immediate vicinity of the crater though some more energetic episodes do occur. In 1984 a more explosive period was documented, during which time large bombs were ejected over a kilometer from the crater.

Between 1972 and 1976 the character of the eruptions was observed to change. The gradual change in eruptive behavior was attributed to a decrease in viscosity. Changes included an apparent change in flow pattern and the audible nature of eruptions. Findings showed that eruptive behavior was largely controlled by the viscosity of the upper part of the magma column. Observed changes in general appearance, size viscosity and eruptive behavior of the Lava Lake suggested a steady increase in the temp of the magma column. The heat most likely being derived from a crystallizing magma chamber at depth (Kyle, P. et al, 1982).

On April 2 2000, the volcano produced a ten-minute episode of harmonic tremor. Although other open-conduit volcanoes routinely exhibit harmonic tremor, they are relatively rare on Erebus despite its nearly constant eruptive state. This event has been interpreted as episodes of dike injection beneath the NorthWest flank of the volcano.

The island is an active, composite strato volcano about 14 km in diameter with a caldera 10 km in diameter. Deception Island has been very active during the last decade and has attracted the attention of many investigators. The most recent eruption from this site was in 1969, when the British Antarctic Survey Base at Whaler’s Bay was destroyed. The deposits here may be ascribed to pre and post caldera events. Pyroclastic rocks predominate, with lava accounting for only 10 - 20% of the exposed part of the volcano (Weaver et al, 1982). Pre-caldera lavas are predominantly basaltic, and there has been a general trend towards a more evolved dacitic composition with time.

Deception Island lavas constitute a virtually unique suite in which unusually high Na₂O contents are associated with comparatively low K₂O values. The precise affinities of the Deception Island volcanic rocks have for some time been a matter of discussion. Analyses of 87Sr/86Sr ratios for rocks from the eruption of 1969 indicate a probable upper mantle source for the magma. (Faure et al, 1972).

The Pleiades are situated near the crest of the Transantarctic Mountain Range in Northern Victoria Land and comprise a part of the Melbourne volcanic province of the upper Cenozoic McMurdo Volcanic Group. The Pleiades consist of a series of scoria cones, endogenous domes, lava flows and associated pyroclastic rocks. They are a series of young eruptive centres perhaps less than 140,000 years old and represent the youngest phases of activity in the 7 million-year history of the Melbourne Volcanic Province.

The location of major volcanic features adjacent to and within the Transantarctic Mountain Range is probably related to deep crustal fractures developed during the Cenozoic uplift of the mountain range. Why volcanism was initiated is unknown, however it may not be coincidence that the bulk of the activity in the McMurdo Volcanic Group has occurred during the last 10 million years (Armstrong, R. L., 1978). This coincides with the full development of the ice sheet on the Eastern Antarctic continental mass and may result from an isostatic depression of the crust due to glacial loading.

Next | Back

Main | Setting | Formation | Geochronology | Palaeogeography | Volcanism | Palaeontology | Maps | References | Links