The youngest pre-caldera volcanism of Deception Island is represented by a thick sequence of subaerial pyroclastic deposits which has been grouped as the Yellow Tuff Formation. Most of these deposits were related to the explosive activity of a central vent which was destroyed during the formation of the caldera. Two members can be distinguished in this formation. The lower member is mainly composed of 1 to 12 m thick massive pyroclastic flow deposits with interbedded air-fall and surge deposits. The upper member is in stratigraphical continuity with the lower member and consists of base surge deposits with minor air-fall and thin pyroclastic flow deposits. The pre-caldera deposits have undergone a palagonitic alteration which produced crystallization of smectites, Fe-oxides, zeolites and calcite.

On 28 March 1982, El Chichon, a volcanic peak located in southern Mexico, began an eruptive phase of activity. Four major eruptions occurred within the next eight days, culminating in a cataclysmic eruption on 4 April. When the dust had settled, an estimated 200 million tons of ash blanketed more than 200 square kilometers of southern Mexico and neighboring Central American countries. Forty thousand villagers were left homeless and several thousand people may have lost their lives. Fifty thousand head of cattle were destroyed outright with many more succumbing to lack of water and pasture. Millions of hectares of crops were destroyed (Figure 1).