The potential causes of temporal changes in volcanic activity in many of the world's volcanic regions are varied and have been the subject of considerable debate (e.g., Matthews, 1969; Kennett and Thunnell, 1977; Grove, 1976; Hein et al., 1978; Rampino et al., 1979; Donn and Ninkovich, 1980; Hall, 1982; Fujioka, 1986; Hardarson and Fitton, 1991; Sigvaldason et al., 1992). The suggestion of causal links between volcanic activity and climatic change is widely upheld. Commonplace is the suggestion that volcanism, by the emission of eruptive gases, induces climate change (Lamb, 1970). Additionally, many workers have indicated, through the effects of glacio- or hydro-isostasy (loading and unloading), that climatic cycles may control volcanic activity (Kennett and Thunnell, 1977; Rampino et al., 1979; McGuire et al., 1997; Sigvaldason et al., 1992). Other workers have suggested that changes in the global rates of volcanic activity are linked to changing activity of the global tectonic system, for example, changes in oceanic spreading rates (Kennett and Thunnell, 1977).
It follows that ongoing assessment of rates of volcanic activity will form a crucial component of this debate, particularly where (1) data are gathered from the continuously accumulating sediments around key volcanic regions and (2) advanced coring methods lead to more complete recovery of the sedimentary record. The effects of variable core recovery on the statistical validity of age-eruption frequency models are discussed by Sigurdsson and Loebner (1981). Although the Pleistocene recovery is generally very good for Leg 186 sites, especially Hole 1150A, sediment loss at depth is not insignificant (Hole 1150A: recovery = 73% from 112 to 722 mbsf; Hole 1151A: recovery = 68% from 78 to 1113 mbsf). This discontinuous recovery hinders evaluation of eruption frequency variations in the pre-~1-Ma record. In addition, a reliable and generally accepted age model for Sites 1150 and 1151 is required before such evaluation and comparison with other sites (see Cadet and Fujioka, 1980; Fujioka, 1986; Cambray et al., 1993) can be attempted.