In 1971 Hudson exploded with a VEI=3 eruption. Although the volcano is not 2000 meters high it covers 300 square kilometers. It is estimated that two eruptions in ~4750 BCE and ~1890 BCE may have been VEI=6s. When Hudson erupted with a VEI=5 in 1991 it was over-shadowed, or perhaps out-clouded, by Pinatubo. There were warning signs for Hudson in late October of 2011: on the 26th October a white column, with little ash, rising to a height of 1.5 km and an earthquake swarm; a cloud of steam and minor ash emissions reached a height of 5.5 km on the 27th. There was no sulphur dioxide detected, the threat level was reduced to 4 (out of 5) and the 45 km exclusion zone remains in place. As the volcano is rather remote the danger to humans from ash fall and lahars is slight, but a massive explosion will cause all sorts of climate and airline problems: ash from 1991 reached the Falklands and Australia.