Delayed deposition of plinian pumice during phreatoplinian volcanism: the 1800-yr-B.P. Taupo eruption, New Zealand

The 1800-yr-B.P. Taupo eruption was one of the most violent and complex rhyolitic explosive eruptions worldwide, in the last 5000 years. The highly energetic Taupo ignimbrite was preceded by 5 phases of plinian and phreatomagmatic fall. The Phase 2 plinian Hatepe Lapilli underlies the phreatoplinian Hatepe and Rotongaio ashes (phases 3 and 4), distinguished by their fine grain size and poor sorting. In a number of proximal localities, outsized plinian pumices occur either within the Rotongaio Ash or at the Rotongaio Ash/Hatepe Ash contact. We interpret these as due to two mechanisms of delayed deposition of pumice originally erupted in Phase 2. A third contrasting type of locality involving delayed deposition of Phase 3 ash during Rotongaio volcanism results from adhering phreatoplinian ash falling or being blown or washed from branches of trees.