New Volcanic Island Unveils Explosive Past

Abstract

A recent volcanic eruption near Tonga in the southwest Pacific created a new island, giving scientists a rare opportunity to explore the volcanic record of this remote region.

Diversity of soluble salt concentrations on volcanic ash aggregates from a variety of eruption types and deposits

“…However, the lower volumes of seawater entrained in the plume during emergence are likely responsible for the overall decrease in salt concentrations with height of the stratigraphy. These results hence suggest an overall decreasing degree of magma-water interaction during progressive emergence, in agreement with Cronin et al (2017).…”

“…The Hunga Tonga-Hunga Ha'apai tuff cone was generated by a series of Surtseyan eruptions that started from a vent at a depth of ~150 m on the floor of the Pacific Ocean 1 km offshore of the islands of Hunga Tonga and Hunga Ha'apai during late 2014-early 2015 (Cronin et al 2017). In a similar fashion to Surtsey (Kokelaar 1986;Cole et al 2001), the Hunga eruptions progressively became emergent with the latest phases occurring within a water-filled subaerial crater (Cronin et al 2017), with the deposit being divided into nine units (U1 through U9).…”

“…The water in the eruptive vent was mainly seawater, possibly chemically modified by interaction with the vent system, rain-fall runoff and leachates from the growing cone around it. In this regard, the tuff cone was subject to significant rain immediately after the cessation of eruptive activity in January 2015, leading to a well-developed erosional rill network (Cronin et al 2017). Surface run-off may have reduced efficient percolation of rain water so that these samples appear only weakly leached.…”

“…This concentration pattern might reflect: (i) variable volumes of seawater involved during each eruptive phase sampled here; (ii) variable efficiency of seawater evaporation during the eruption sequence; or (iii) changes in the seawater composition. As the eruption progressed, it clearly became emergent (Cronin et al 2017), thus less and less seawater was entrained in the plume. On the one hand, this "drying" process favors more efficient seawater evaporation because the particles stay hotter for longer due to the lower water:pyroclast ratios.…”

Iceland drilling project aims to unearth how islands form

“…That's in stark contrast to many volcanic islands, such as one that appeared near Tonga in 2014 but has already eroded by 40% (ref. 3). "Because the vast majority of these islands disappear, we most likely substantially underestimate the number and volume of eruptions occurring at or just below sea level in the ocean, and hence the associated volcanic risk, " says Nico Fournier, a volcanologist with the GNS Science research institute in Taupo, New Zealand.…”