The geology and volcanic geomorphology of Heard Island

[Extract] If weather permits, Heard Island leaves lasting visual impressions. From the colossal ice-sheathed bulk of the Big Ben volcano down to the hostile coast with glaciers, ice cliffs, promontories and stormy seas, the island is dramatic. A basement of stratified rocks occurs in the northern parts of the island, raising exciting possibilities for direct examination of some of the early geological history of this region of the Southern Ocean. The discovery of the island, and an account of its earliest visitors, are given by Downes and Downes (2005) and Green (2005). Heard Island is located on the relatively shallow central part of the extensive submarine Kerguelen Plateau. It is one of the largest submarine plateaus on earth, and has a geological history extending over 115 m.y. (Davies et al. 1989). In reviewing the geological evolution of the Kerguelen Plateau, Quilty (2005) has emphasized how Heard and the McDonald Islands can provide special data, in parallel to the regional information derived from the Ocean Drilling Program. The islands permit direct access to more extensive outcrops, for a fuller understanding of their local variations and geological context. Conversely, the thickened oceanic crust of the plateau is an atypical substrate for an ocean island volcano and may have contributed to some of the unique features of Heard Island geology and geochemistry. The present chapter sets out to describe what is currently known about Heard Island geology