“
“A quantitative understanding of hydrology is important for resource SP600125 in vivo management in all island settings (e.g. Bahamas, Whitaker and Smart (1997); Malta, Stuart et al. (2010)). In many volcanic island

terrains, including the Lesser Antilles arc island of Montserrat, high permeability surface geology generates limited and ephemeral drainage systems (Peterson, 1972 and Cabrera and Custodio, 2004). In such environments water supplies often rely entirely on the productivity of springs and abstraction from other parts of the groundwater system. In active volcanic island settings the involvement of groundwater in volcanic processes can destabilise the edifice and generate explosive phreatic eruptions (Germanovich and Lowell, 1995, Bleomycin in vivo Reid et al., 2001 and Fournier et al., 2010). Hydrological systems have also been observed to respond to volcanic perturbations (Shibata and Akita, 2001, Hurwitz and Johnston, 2003 and Kopylova and Boldina, 2012). It is, therefore, possible that the hydrological system may provide valuable information about the state of a restless volcano prior to eruption. Hautmann et al. (2010) proposed that groundwater movement, in response to changes in volcanic activity may be responsible for residual gravity anomalies recorded on Montserrat between 2006 and 2008. The potential

for groundwater perturbations to precede an eruption (e.g. Usu, Japan; Shibata and Akita, 2001) and generate recordable geophysical signals that contain information about active state of a volcano, demonstrates that understanding the hydrological system in volcanic settings the is essential for the development and correct interpretation of a truly multi-parameter, hazard

monitoring dataset. Existing conceptual models describing the hydrogeology of small volcanic islands are based on observations from basaltic, ocean island volcanoes, dominated by relatively permeable basalt lava flows. Cruz and Silva (2001) highlight two major and conflicting conceptual models for such settings: the Hawaiian model and the Canary Island model. The Hawaiian model describes a low-lying, basal water table aquifer with high-level water bodies perched on low permeability ash or soil beds and impounded by dykes (Peterson, 1972 and Ingebritsen and Scholl, 1993). A coastal borehole drilled as part of the Hawaii Scientific Drilling Project in 1993 encountered three freshwater aquifers, each overlying saline to brackish groundwaters, separated by leaky aquitards of soil and ash horizons or calcareous sediments (Thomas et al., 1996). Thomas et al. (1996) propose that soil layers and extensive ash beds are responsible for elevating inland ground water levels. A borehole drilled at 1102 m amsl, 14 km inland, near the summit of Kilauea volcano, encountered the water table at just 610 m amsl (Keller et al., 1979). The Hawaiian model has been used to describe the conceptual hydrology of Cape Verde Islands (Heilweil et al., 2009).