Isotope tracer methods were used to determine flow paths, recharge areas, and relative age for groundwater in the Kilauea volcano area of the Island of Hawaii. A network of up to 66 precipitation collectors was emplaced in the study area and sampled twice yearly for a 3-year period. Stable isotopes in rainfall show three distinct isotopic gradients with elevation, which are correlated with trade wind, rain shadow, and highelevation climatological patterns. Temporal variations in precipitation isotopes are controlled more by the frequency of storms than by seasonal temperature fluctuations. Results from this study suggest that (1) sampling network design must take into account areal variations in rainfall patterns on islands and in continental coastal areas and (2) isotope/elevation gradients on other tropical islands may be predictable on the basis of similar climatology. Groundwater was sampled yearly in coastal springs, wells, and a few high-elevation springs. Areal contrasts in groundwater stable isotopes and tritium indicate that the volcanic rift zones compartmentalize the regional groundwater system, isolating the groundwater south of Kilauea's summit and rift zones. Part of the Southwest Rift Zone appears to act as a conduit for water from higher elevation, but there is no evidence for downrift flow in the springs and shallow wells sampled in the lower East Rift Zone. [Yurtsever and Gat, 1981; Dansgaard, 1964].In the southeastern part of the Island of Hawaii, comprising Kilauea volcano and the surrounding flanks of Mauna Loa volcano (Figure 1), perennial streams are absent despite an average rainfall of about 2000 mm/yr. Wells are generally located within 10 km Of the coastline (below approximately 300 m in elevation), and there are no wells in a large part of the area. As a result, groundwater flow patterns in and around Kilauea volcano are not well known. The purpose of this study was twofold: (1) to use isotope techniques to interpret the hydrology of the Kilauea volcano area, particularly with regard to determining the regional hydrologic setting for Kilauea's geothermal systems, and (2) to determine precipitation isotope variation in an area with highly variable rainfall patterns, so the findings can be used in hydrologic studies in areas with similar climatology.

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[1] This paper quantifies atmospheric mercury (Hg) emissions from substrates and fumaroles associated with three hydrothermal systems: Lassen Volcanic Center, California (LVC); Yellowstone Caldera, Wyoming (YC); and Dixie Valley, Nevada (DV). Substrate Hg fluxes were measured using field chamber methods at thermal and nonthermal sites. The highest Hg fluxes (up to 541 ng m À2 h À1 ) were measured at thermal active areas. Fluxes from altered and unaltered nonthermal sites were <10 ng m À2 h À1 and were comparable to those measured in natural low-Hg background regions for YC and DV, and at LVC they were slightly elevated. Similarly, reactive gaseous mercury concentrations were higher in thermal active areas. Using a Geographic Information System framework for scaling, estimated area-average Hg emissions from substrates were 0.9-3.8 ng m À2 h À1at LVC, 0.8-2.8 ng m À2 h À1 at YC, and 0.4-0.5 ng m À2 h À1 at DV. At LVC, nonthermal areas were the primary substrate source of atmospheric Hg (>98%). At YC, substrate Hg emissions were dominated (50 to 90%) by acidically altered thermal areas. Substrate emissions at DV were low and primarily from nonthermal areas (66% to 75%). Fumarole emissions at LVC (91-146 kg yr À1 ) and YC (0.18-1.6 kg yr À1 for Mud Volcano) were estimated by applying Hg:H 2 O and Hg:CO 2 ratios in hydrothermal gas samples to H 2 O and CO 2 emissions. Applying total area-average emissions from substrates and thermal features at LVC, YC, and DV to similar systems across the conterminous United States, yearly atmospheric Hg emissions from active hydrothermal systems are projected to be 1.3-2.1 Mg.

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Between 1992 and 1998, we sampled gas discharges from ≤173°C fumaroles and springs at 12 quiescent but potentially restless volcanoes in the Cascade Range and Aleutian Arc (CRAA) including