A study of leaching of freshly erupted basaltic and dacitic air-fall ash and bomb fragment samples, unaffected by rain, shows that glass dissolution is the dominant process by which uranium is initially mobilized from air-fall volcanic ash. Si, Li, and V are also preferentially mobilized by glass dissolution. Gaseous transfer followed by fixation of soluble uranium species on volcanic-ash particles is not an important process affecting uranium mobility. Gaseous transfer, however, may be important in forming water-soluble phases, adsorbed to ash surfaces, enriched in the economically and environmentally important elements Zn, Cu, Cd, Pb, B, F, and Ba. Quick removal of these adsorbed elements by the first exposure of freshly erupted ash to rain and surface water may pose short-term hazards to certain forms of aquatic and terrestrial life. Such rapid release of material may also represent the first step in transportation of economically important elements to environments favorable for precipitation into deposits of commercial interest. Ash samples collected from the active Guatemalan volcanoes Fuego and Pacaya (high-Al basalts) and Santiaguito (hornblende-hypersthene dacite); bomb fragments from Augustine volcano (andesite-dacite), Alaska, and Heimaey (basalt), Vestmann Islands, Iceland; and fragments of "rhyolitic" pumice from various historic eruptions were subjected to three successive leaches with a constant water-to-ash weight ratio of 4:1. The volcanic material was successively leached by: (1) distilled-deionized water (pH = 5.0-5.5) at room temperature for 24 h, which removes water-soluble gases and salts adsorbed on ash surfaces during eruption; (2) dilute HCl solution (pH = 3.5-4.0) at room temperature for 24 h, which continues the attack initiated by the water and also attacks acid-soluble sulfides and oxides; (3) a solution 0.05 M in both Na,CO, and NaHCO, (pH = 9.9) at 80°C for one week, which preferentially dissolves volcanic glass. The first two leaches mimic interaction of ash with rain produced in the vicinity of an active eruption. The third leach accelerates the effect of prolonged contact of volcanic ash with alkaline ground water present during ash diagenesis.

Journal of Volcanology and Geothermal Research↗

USGS1979

The flow mechanism in the Chalk based on radio-isotope analyses of groundwater in the London Basin

14 C analyses of groundwaters from the Chalk of the London Basin are re-interpreted and the age of the groundwater is revised. Radio-isotope analyses are used to examine the flow mechanism in the aquifer. The evidence supports the view that a network of micro-fissures and larger intergranular pores in the matrix provides a significant part of the water pumped from Chalk wells and the major fissures distribute the water to the wells. Most of the matrix is fine-grained and contains a very old water. This diffuses into the micro-fissures and larger pores and is carried to the wells by the major fissures.

southeast England↗

USGS1977

The age of groundwater in the Lincolnshire Limestone, England and its relevance to the flow mechanism

Groundwater samples from the Lincolnshire Limestone have been analysed for tritium, radiocarbon, and the stable-isotope ratios 13 C 12 C "> 13 C 12 C , 18 O 16 O "> 18 O 16 O and D/H. The age of the water increases in a downgradient direction below overlying confining deposits and reaches a maximum age greater than 25,000 years within 15 km of the outcrop. The δ 13 C ratio ultimately attains the unusually low negative values of −2‰ in a downgradient direction; this is approaching that of the aquifer matrix which is +2.35‰. The reason is believed to be exchange of carbon between the groundwater and the matrix by a continuous process of precipitation and further solution of calcium carbonate. The δ 18 O and δ D ratios imply that recharge of the aquifer during the late Pleistocene took place in the spring and autumn rather than the winter as at present. The data are interpreted by assuming that movement of water through the saturated zone is a combination of flow in fissures and “piston flow” through the micro-fissures and pores of the rock. The mechanism of water movement in the saturated zone is dominated by relatively rapid flow in fissures, but the fissure flow includes a contribution of much older water from “intergranular” storage which enters the fissures from the rock matrix by pressure differentials in the fissure distribution system and by diffusion. The distribution of water of different ages in the aquifer is closely related to recent groundwater abstraction patterns.

Journal of Hydrology↗