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Through weathering processes, volcanic rocks contribute both to nutrient flux into the biosphere and atmospheric CO 2 drawdown. As rhyolitic rocks are of higher silica content and have lower concentrations of biologically-important elements than basalts they might be expected to be less easily weathered by a biota. Investigations on the microbial diversity and weathering of silica-rich rhyolitic glass (obsidian) from a lava flow in Iceland are reported. 16S rDNA analysis of rock whole genome DNA shows that the rock hosts remarkable eubacterial diversity. Irregular pitted weathering textures correspond to regions of eubacterial colonization as shown by FISH. Weathering processes proceed at alteration fronts, with a preference for potentially nutrient-rich regions containing plagioclase and pyroxene crystals, although these features are less well defined than those previously reported from basaltic glass, consistent with the lower rates of chemical weathering previously reported for rhyolites compared to ba...

The c. AD 1305 Kaharoa eruptive episode consisted of a complex sequence of basalt‐triggered high‐silica rhyolite eruptions from at least seven vents along an 8 km linear zone across Tarawera Volcano. Initial plinian eruptions from a summit vent spread Kaharoa Tephra southeast across the North Island, accompanied by phreatomagmatic explosions and pyroclastic density currents from vents opened on the northern flanks of the volcano. The early plinian phase was ended by extrusion of Crater Dome in the summit vent, with explosive activity migrating to two adjacent vents (Tarawera and Ruawahia) to the southwest and northeast. Renewed plinian eruptions, apparently from the northern vents, produced tephra falls dispersed northeast‐northwest from the volcano. Extrusion of the three summit lava domes was accompanied by voluminous block‐and‐ash flows generated by collapse of the growing Ruawahia and Wahanga Domes, forming large fans to north, southeast, and northwest of the volcano. Calculation of Kaharoa l...

The March 1974 vulcanian-type eruption of Ngauruhoe produced a small air-fall deposit of andesitic ash with a volume of 0.0005 km3.

We propose that various rhyolitic pumice deposits in the Taupo Volcanic Zone and beyond, that were previously called Wairakei Breccia, Waitahanui Breccia (in part), Oruanui (Pumice) Formation, and Kawakawa Tephra Formation, are the products of one large eruption at 20 000 years B.P. On grounds of precedence we name these voluminous deposits Wairakei Formation and suggest that other names be made redundant. Correlations across New Zealand and into the Southwest Pacific basin are presented, together with data from a stratigraphic drillhole near Taupo. The large volume of water inferred to have taken part in magma-water explosive interaction came from proto-Lake Taupo. The correlation of these 20 000 year old deposits, previously thought to be different ages, has a bearing on the age of the Huka Falls Formation and the late Quaternary history of the Taupo district and the Waikato River.