| Summary: | International Symposium on the Activity of Oceanic Volcanoes. Ponta Delgada, 4-9 August 1980. On the oceanic islands of the Atlantic ignimbrites are known to occur on Iceland, Gran Canaria, Tenerife and on two of the Azores islands, Terceira and São Miguel. Ignimbrite may form a larger proportion of the total volume of rock on the island of Terceira than it does on any of the other islands, yet the individual eruption volumes are small (≤ 1 km³). There have been at least 6 major ignimbrite forming eruptions during the islands' history, and older ash-fall sequences may provide evidence of several others. The two youngest ignimbrites, the Lajes (23,000yBP) and the Angra (19,000yBP) resulted from caldera-forming eruptions of Pico Alto volcano, a «parasitic» caldera on the north flanks of the older Guilherme Moniz volcano. Both pyroclastic flows reached the edge of the island and much o-f the deposition was probably submarine. The cooling units are relatively thin (1-20 m), but the Lajes is densely welded, a feature typical of highly alkaline ignimbrites. […]. info:eu-repo/semantics/publishedVersion
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