PYROCLASTIC STRATIGRAPHY OF THE SOUFRIERE HILLS VOLCANO, MONTSERRAT -IMPLICATIONS FOR THE PRESENT ERUPTION

The stratigraphy of the Soufriere Hills volcano is dominated by dense- andesite block and ash flow deposits. Forty-one radiocarbon ages permi t a reconstruction of the eruptive history over the past 31,000 years. A single stratigraphic member yielding radiocarbon ages of 22,000 to 20,000 years B.P. is composed of block and ash flow deposits with semi -vesiculated clasts concentrated in the upper third of each deposit. T he present eruption is also producing block and ash flow deposits with both dense and semi-vesiculated clasts. It marks a return to a more e xplosive driven type of activity as occurred 22,000 to 20,000 years ag o. Deposits of this member have a broad sheet-like form and volumes in excess of any produced so far by the present eruption.