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. […].