NEVIS GEOLOGY

Geology of the island has been subdivided into seven volcanic centers, now mainly represented by lava domes and their associated primary (e.g. block and ash flows) and secondary deposits (e.g. lahars). The oldest deposits described from the island are blocks of crystalline limestone containing mid-Eocene fossils contained in a conglomerate unit (Hutton, 1965). The seven volcanic centers, arranged in order of decreasing age are Round Hill (3.43 0.17 Ma), Cades Bay (3.22 0.16 Ma), Hurricane Hill (2.70 0.50 Ma), Saddle Hill (1.80 0.30 Ma), Butlers Mountain (1.10 0.16 Ma), Red Cliff, and Nevis Peak (main cone-0.98 0.10, Mt. Lily welded tuff-0.23 0.16, intracrater dome-0.10 0.06 Ma). No ages have been obtained for the volcanic breccias of Red Hill, which is thought to be the remnant of a volcanic cone originally located off the east coast. The relative freshness of the deposits from Red Hill led Hutton and Nockolds (1978) to suggest that they were of comparable age to the deposits from Nevis Peak. The composition of essentially all of the centers are porphyritic dacites containing a combination of hornblende, orthopyroxene and clinoproxene phenocrysts.

There have been no historical eruptions on Nevis, however the island does have two main areas of hydrothermal activity, Cades Bay, which formed in 1953 and had temperatures in the range 96-100˚C (Lindsay, 2001) and Farm Estate Soufriere for which temperatures between 53-93˚C have been recorded (Lindsay, 2001). The island has also experienced shallow (1-11 km depth) earthquake swarms in 1926, 1947-48, 1950-51, and 1961-63.