Rapid, multichannel monitoring of fumaroles on Volcfin Colima, Mexico, provides new insight into the timescales and magnitudes of fumarole temperature variation. Temperatures in five fumaroles, all located along a single fracture cutting the summit lava dome of the volcano, were monitored at 20-min inte•wals between May 1991 and May 1992. Measurements were made using a programmable data logger deployed near the fumarole field, and data were radiotelemetered to a nearby volcano observatory at regular intervals. Mean fumarole temperatures varied between 350øC and 550øC. Statistical analysis of these time series shows that significant diurual variation occurs in each fumarole. Magnitudes of these daily fluctuations are generally between 25øC and 50øC, although larger-amplitude variations occur, especially in cooler fumaroles. Simultaneous monitoring of atmospheric pressure at the fumaroles indicates that these variations in temperature are inversely correlated with barometric pressure. These observations indicate that fumarole temperatures respond to atmospheric forcing. A nmnerical model developed to explore the dependence of fumarole temperature on mass flow demonstrates that many aspects of observed temperature variation are accounted for by mass flow variation, resulting from small changes in barometric pressure. The relationship between mass flow and fumarole temperature is nonlinear: the response of fumarole temperatures to a given change in mass flow is greatest in fumaroles with low mass flow (and cool temperatures). The nature of this dependence is little affected by fumarole geometry for the cases considered. Colima, average temperatures changed by less than 100øC during the 1-year sampling period. During and immediately following effusive activity, changes in degassing were abrupt and inconsistent along the length of the fracture. Following this period, temperatures decreased gradually, and there was a higher degree of correlation between fumaroles. The method described here represents a substantial improvement over traditional fumarole-monitoring techniques because subtle variation can be quickly identified using standard statistical techniques, and the method provides regular information about thermal activity on a volcano, minimizing the hazards normally associated with the collection of these data on a regular basis. Continuous measurement of fumarole temperatures may be an effective means of monitoring local mass flow on volcanoes. At Volcfin

Abltract. Atomic Ruorescence-based metnods nave been developed for measuring ultratrace level. of mercury (Hg) in environmental (water, soil) and biological (fisn tissue) samplea. In addition, metnods for preparation of water, soil, and tinus samples nave been developed. For tne analysis of total Hg in soil, sediment and fisn tne samples are digested with concentrated nitric aCId in saaled glass ampulas, and subsequently autoclaved. Water samples are digested using standard brominating procedures. A Merlin Plus, PS Analytical atomic fluorescence spectromete, (AFS) system equipped with an autoaampler, vapor generator, fluorescence detector and a PC based integrator package ia used in tne determination of total Hg. Tne determinetion of Hg mercury species in water, witnout pra-derivatization, involves adsorbant pre-concentration of tne organomarcurials onto sulfydryl-cotton fibers. Tha organic Hg compounds are alutad with a small volume of acidic KBr and CuSO. and extracted into dichloromethane. Sediment, soil and tissua samples are homogenizad and the organomercurials first released from the sample by the combined action of ecidic KBr and CuSO. and extracted into dichloromethane. The initial extracts are subjected to tniosulfate clean-up and tne organomercury species are iaolated as tneir chloride derivatives by cupric chloride eddition anei subsequent extraction into a small volume of dichlorometnane. Analyais of organic Hg compounda is accomplisned by capillary column chromatograpny coupled witn atomic fluorescenca detection.

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The only reported occurrence of quartz‐rich sands in Jamaica is on the plains of Black River, St Elizabeth, where they outcrop in isolated pockets. The sands overlie limestones of the White Limestone Supergroup and the Coastal Group, and partly underlie Holocene peat deposits. Monocrystalline quartz, containing fluid and mineral inclusions, is the dominant mineral of the sands, with the heavy minerals. magnetite, haematite, epidote, rutile, anatase, zircon and tourmaline, occurring in minor amounts. Grain surface texture studies of the quartz grains have identified a series of mechanical and chemical features. Microtextures depicting marine, aeolian and pedological environments have been retained on the grains and represent the last three stages in the history of the grains. The petrography of the sands indicates an igneous provenance, with the major source of the detrital minerals being the Cretaceous granitoids that outcrop in the eastern half of the island. These rocks were unroofed during the uplift of Jamaica in the Late Tertiary and were subjected to extensive chemical weathering, which accounted for the breakdown of the majority of their primary silicate minerals. Fluvial transportation and deposition of detritus onto the shelf of the south coast commenced during this period and continued into the Pleistocene, providing terrigenous sand that was modified along the coast to quartz arenite by moderate to high energy marine conditions. Tidal currents, east‐west longshore currents and weathering contributed to the maturity of the sand by the time it had been transported along the shelf to the vicinity of Black River. During low sea level stands in the Pleistocene, some of this sediment that became trapped on the shelf was blown inland by south‐east winds.