Bill Evans, PhD (Former Employee)

Six natural gas manifestions from the upper Tiber Valley at Caprese Michelangela and Pieve S. Stefano (Arezzo) and at Umbertide (Pertugia) localities have been analysed for major, minor, trace gas compositions, as well as for ??13C in CO2 and CH4, ??15N in N2 and 3He/4He isotopic ratios. All gas emissions are CO2-rich (???94%), with N2 contents of 4-5%. Those from Caprese and Pieve S...

Gas manifestations in north-central Italy consist of CO2-rich gases with minor N2-rich emissions and discharge either along with thermal springs or into cold and stagnant waters. 'Cold' gases are prevalently CO2-dominated (> 90%) while gases related to the thermal waters have variable composition: from CO2 > 99.5% to N2 > 90%. The variable composition of 'thermal' gases is caused by...

Fluids associated with the San Andreas and companion faults n central and south-central California have high 3He/4He ratios. The lack of correlation between helium isotopes and fluid chemistry or local geology requires that fluids enter the fault system from the mantle. Mantle fluids passing through the ductile lower crust must enter the brittle fault zone at or near lithostatic...

No abstract available.

No abstract available.

Since 1980, scientists have monitored geologic unrest in Long Valley Caldera and at adjacent Mammoth Mountain, California. After a persistent swarm of earthquakes beneath Mammoth Mountain in 1989, earth scientists discovered that large volumes of carbon dioxide (CO2) gas were seeping from beneath this volcano. This gas is killing trees on the mountain and also can be a danger to people...

Results of the chemical and isotopic analysis of the water and gases discharged from volcanic crater lakes and soda springs located along the Cameroon Volcanic Line were used to characterize and infer their genetic relationships. Variations in the solute compositions of the waters indicate the dominant influence of silicate hydrolysis. Na+ (40-95%) constitutes the major cation in the...

Radon emanation has been observed to be anomalously high along active faults in many parts of the world. We tested this relationship by conducting and repeating soil air radon surveys with a portable radon meter across several faults in California. The results confirm the existence of fault-associated radon anomalies, which show characteristic features that may be related to fault...

Mammoth Mountain, in the western United States, is a large dacitic volcano with a long history of volcanism that began 200 kyr ago and produced phreatic eruptions as recently as 500 ± 200 yr BP. Seismicity, ground deformation and changes in fumarole gas composition suggested an episode of shallow dyke intrusion in 1989–90. Areas of dying forest and incidents of near asphyxia in confined...

No abstract available.

Hot springs along the Owyhee River in southeastern Oregon between Three Forks and Lake Owyhee could be part of a north flowing regional system or a series of small separate geothermal systems Heat for the waters could be from a very young (Holocene) volcanic activity (basalt flows) of the Owyhee Uplands or the regional heat flow. The springs discharge warm to hot, dilute, slightly...

The catastrophic release of gas from Lake Nyos, Cameroon, in 1986 caused substantial but incomplete mixing of the stratified water column. The post-release evolution of water-column structure has been monitored through April 1992. Changes began immediately after the event as rainfall and inflow brought dilute fluid into the surface layer. Inflow and surface mixing have gradually deepened...