Fire in the sea—Growth and destruction of submarine volcanoes

Abstract

381 The appearance of a steaming volcano close to the sea surface represents a rare but spectacular geological event, because the birth of a new volcano vividly illustrates the steady yet piecemeal growth of the Earth’s crust; and its simultaneous destruction. Every volcanic eruption on land generates a quantum jump in our understanding of growth and destructive processes of volcanoes, but this is even more true underwater, although eruptions typically occur hidden from view. Loihi Seamount, ~35 km off the southeast coast of the Big Island of Hawaii, has for many years been an instructive example. The broad range in composition of its basalts greatly changed views of the compositional evolution of Hawaii and other oceanic islands, and led to the discovery of a range of volcaniclastic products, from glassy ash to basalt breccias (Garcia et al., 1998; Clague et al., 2003). Loihi experienced an eruption in 1996, followed by massive collapse of its top, but this top is located almost 1000 m below sea level, making regular, detailed observations diffi cult to almost impossible, if only because of the very high costs. The top of the active submarine volcano Monowai in the Kermadec Arc (north of New Zealand) rises episodically close to the water surface, changing rapidly (weeks to decades) in elevation by tens of meters, because of repeated episodes of volcano growth and rapid fl ank collapse (Wright et al., 2008; Watts et al., 2012). Growth and collapse rates at Monowai were very high, with the volume changes calculated as 0.11 km 3 yr -1 for collapse, and 0.63 km 3 yr