The depth to the water table is 23 m below ground surface (HydroSource, 2004). This equates to an elevation of about 12 m amsl, consistent with the observations from the older, now buried, wells in the Belham Valley (Maxim Engineering, 1995 and Davies find more and Peart, 2003). Both the Hawaiian model (Peterson, 1972 and Ingebritsen and Scholl, 1993) and the Canary Island model (Cabrera and Custodio, 2004 and Custodio, 2007) allow for such a low lying water table towards the coast. The models diverge in their conceptualisation of the hydrology towards the interior of the islands. In the Hawaiian Model (corresponding to Robins et al. (1990)’s Type 2), the water table remains at low

elevation under the islands interior, and springs at higher elevation are fed by aquifers perched on ash layers and buried soils and impounded by intrusive, volcanic dykes.

In the Canary Islands model (corresponding to Robins et al. (1990)’s Type 1), the occurrence of high-elevation aquifers is related to steep doming of the water table over low permeability volcanic cores, and the only truly perched aquifers are localised and small. Robins et al. (1990)’s Type 1 has previously been applied to Montserrat (Davies and Peart, 2003). Under either regime, the presence of the springs at relatively high elevations (Fig. 13) SB203580 in vivo on the flanks of CH and SHV (pre-eruption) (Fig. 12) requires the existence of lower permeability beneath the high permeability surface lithologies. The magnitude Miconazole of spring yields on Montserrat suggests that

the source aquifers are reasonably extensive and therefore any low permeability features must be relativity laterally continuous. Using an annual recharge of 0.27 m/yr, from our recharge model estimates, and assuming that all recharge to the spring catchment discharges at the spring site, the recharge area required to match 18 L/s production observed at Killiekrankie spring is over 2 km2. This is over 40 times the topographically defined catchment for Killiekrankie, as estimated from a digital elevation model (DEM). Even if we use a recharge close to the annual rainfall average at Hope rain gauge (2 m/yr), the necessary recharge area still over 5 times the spring’s topographically defined catchment. The aquifers that supply the springs, and therefore any low permeability unit, must extend beyond the topographically defined catchment. In a Canary Island-type (Type 1) model intrusive volcanic cores provide a laterally continuous, low permeability unit that causes the water table to dome steeply to high elevations. In the Canaries this results in the development of high elevation aquifers that are exploited by tunnels and galleries (Carracedo, 1994). It is probable that within the central cores of Montserrat’s extinct volcanic complexes there exist similar, low permeability intrusive bodies that once fed the eruptions.