19). Type 2 differs from Type 1 in that aquifers supplying the high elevation springs are perched or impounded within a vadose zone that is several hundreds of metres thick. Under this regime the units beneath the perching aquitard would be unsaturated. An unpublished commercial report (Maxim Engineering, 1995) GSK 3 inhibitor states that a 1967/1968 water test well located in a ghaut on the northern slopes of CH at ∼200 m amsl was drilled to a depth of 75 m amsl and did not encounter saturated material. Up-valley of this drill site

at the elevations of 315 and 345 m amsl the ghaut is fed by Blackwood Allan and Mongo Springs. In the Type 2 model the spring aquifers are hydraulically connected to the deeper hydrological system and to low elevation coastal aquifers. Under these conditions spring behaviour, temperature and composition is hydraulically coupled with groundwater

conditions and pressure at depth, and therefore to volcanic perturbation. By defining hydraulic connectivity between low and high elevation aquifers, this model can better explain the anomalously warm springs at high elevation on the south side of CH. Certain observations from Montserrat are consistent with either of the major volcanic island conceptual hydrology models. Without deep boreholes within the central portions of Montserrat’s volcanic complexes it is difficult to definitively propose which model best represents the hydrology of this volcanic arc island. Both should be maintained as working hypotheses, with a view to gathering data to better constrain the system. High yielding springs on the flanks of the extinct INK 128 mw Centre Hills volcanic complex and low lying aquifers in more distal locations provide an essential water

resource to the island’s population, as it recovers from over 15 years of volcanic activity. Recharge models predict annual recharge of 10–20% of annual rainfall with a strong seasonality; models predict that over 70% of the islands recharge occurs between July and December. Land use is a critical control on recharge; during extended periods of quiescence changes ADAMTS5 in vegetation type, including colonisation and eventual afforestation of young deposits in the south, and deforestation for agriculture around Centre Hills, are expected to modify the current recharge conditions. Recharge will also be affected by any fluctuations in rainfall patterns associated with climate change; this will, no doubt, have implications for spring yield. The development of springs at elevations of 200–400 m amsl, on an island with only ephemeral rivers and no other surface water, requires the presence of low permeability units. Assuming a recharge rate of 0.27 m/yr the surface recharge area required to supply the highest yielding spring on Montserrat is over 40 times the topographically defined catchment.