Geology topics

F. Murphy

Publications and source records attributed to F. Murphy.

5 recordsLinked to original sources

USGS2007

A sample-freezing drive shoe for a wire line piston core sampler

Loss of fluids and samples during retrieval of cores of saturated, noncohesive sediments results in incorrect measures of fluid distributions and an inaccurate measure of the stratigraphic position of the sample. To reduce these errors, we developed a hollow drive shoe that freezes in place the lowest 3 inches (75 mm) of a 1.88‐inch‐diameter (48 mm), 5‐foot‐long (1.5 m) sediment sample taken using a commercial wire line piston core smapler. The end of the core is frozen by piping liquid carbon dioxide at ambient temperature through a steel tube from a bottle at the land surface to the drive shoe where it evaporates and expands, cooling the interior surface of the shoe to about ‐ 109°F (‐ 78°C). Freezing a core end takes about 10 minutes. The device was used to collect samples for a study of oil‐water‐air distributions, and for studies of water chemistry and microbial activity in unconsolidated sediments at the site of an oil spill near Bemidji, Minnesota. Before freezing was employed, samples of sandy sediments from near the water table sometimes flowed out of the core barrel as the sampler was withdrawn. Freezing the bottom of the core allowed for the retention of all material that entered the core barrel and lessened the redistribution of fluids within the core. The device is useful in the unsaturated and shallow saturated zones, but does not freeze cores well at depths greater than about 20 feet (6 m) below water, possibly because the feed tube plugs with dry ice with increased exhaust back‐pressure, or because sediment enters the annulus between the core barrel and the core barrel liner and blocks the exhaust.

Ground Water Monitoring and Remediation↗

USGS2005

U/Th dating by SHRIMP RG ion-microprobe mass spectrometry using single ion-exchange beads

We present a new analytical method for U-series isotopes using the SHRIMP RG (Sensitive High mass Resolution Ion MicroProbe) mass spectrometer that utilizes the preconcentration of the U-series isotopes from a sample onto a single ion-exchange bead. Ion-microprobe mass spectrometry is capable of producing Th ionization efficiencies in excess of 2%. Analytical precision is typically better than alpha spectroscopy, but not as good as thermal ionization mass spectroscopy (TIMS) and inductively coupled plasma multicollector mass spectrometry (ICP-MS). Like TIMS and ICP-MS the method allows analysis of small samples sizes, but also adds the advantage of rapidity of analysis. A major advantage of ion-microprobe analysis is that U and Th isotopes are analyzed in the same bead, simplifying the process of chemical separation. Analytical time on the instrument is ???60 min per sample, and a single instrument-loading can accommodate 15-20 samples to be analyzed in a 24-h day. An additional advantage is that the method allows multiple reanalyses of the same bead and that samples can be archived for reanalysis at a later time. Because the ion beam excavates a pit only a few ??m deep, the mount can later be repolished and reanalyzed numerous times. The method described of preconcentrating a low concentration sample onto a small conductive substrate to allow ion-microprobe mass spectrometry is potentially applicable to many other systems. Copyright ?? 2005 Elsevier Ltd.

Geochimica et Cosmochimica Acta↗

USGS1991

The temperature dependence of ponded infiltration under isothermal conditions

A simple temperature-sensitive modification to the Green and Ampt infiltration equation is described; this assumes that the temperature dependence of the hydraulic conductivity is reciprocally equal to the temperature dependence of the viscosity of liquid water, and that both the transmission zone saturation and the wetting front matric potential gradient are independent of temperature. This modified Green and Ampt equation is compared with ponded, isothermal infiltration experiments run on repacked columns of Olympic Sand and Aiken Loam at 5, 25, and 60°C. Experimental results showed increases in infiltration rates of at least 300% between 5 and 60°C for both soil materials, with subsequent increases in cumulative infiltration of even greater magnitudes for the loam. There is good agreement between measured and predicted initial infiltration rates at 25°C for both soil materials, yet at 60°C, the predicted results overestimate initial infiltration rates for the sand and underestimate initial rates for the loam. Measurements of the wetting depth vs. cumulative infiltration indicate that the transmission zone saturation increased with increasing temperature for both soil materials. In spite of this increased saturation with temperature, the final infiltration rates at both 25 and 60°C were predicted accurately using the modified Green and Ampt equation. This suggests that increased saturation occurred primarily in dead-end pore spaces, so that transmission zone hydraulic conductivities were unaffected by these temperature-induced changes in saturation. In conclusion, except for initial infiltration rates at 60°C, the measured influence of temperature on infiltration rates was fully accounted for by the temperature dependence of the viscosity of liquid water.

Journal of Hydrology↗

USGS1990

Monitoring moisture storage in trees using time domain reflectometry

Laboratory and field tests were performed to examine the feasibility of using time domain reflectometry (TDR) to monitor changes in the moisture storage of the woody parts of trees. To serve as wave guides for the TDR signal, pairs of stainless steel rods (13 cm long, 0.32 cm in diameter, and 2.5 cm separation) were driven into parallel pilot holes drilled into the woody parts of trees, and a cable testing oscilloscope was used to determine the apparent dielectric constant. A laboratory calibration test was performed on two sapwood samples, so that the relation between the volumetric water content and the apparent dielectric constant of the sapwood could be determined over a range of water contents. The resulting calibration curve for these sapwood samples was significantly different than the general calibration curve used for soils, showing a smaller change in the apparent dielectric constant for a given change in the volumetric water content than is typical for soils. The calibration curve was used to estimate the average volumetric water content to a depth of 13 cm in living trees. One field experiment was conducted on an English walnut tree ( Juglans regia ) with a diameter of 40 cm, growing in a flood-irrigated orchard on a Hanford sandy loam near Modesto, California (U.S.A.). Rods were driven into the tree at about 50 cm above the soil surface and monitored hourly for the month of August, 1988. The moisture content determined by TDR showed a gradual decrease from 0.44 to 0.42 cm 3 cm −3 over a two week period prior to flood irrigation, followed by a rapid rise to 0.47 cm 3 cm −3 over a four day period after irrigation, then again a gradual decline approaching the next irrigation. A second field experiment was made on ten evergreen and deciduous trees with diameters ranging from 30 to 120 cm, growing in the foothills of the Coast Range of central California. Rods were driven into each tree at 50 to 100 cm above the soil surface and monitored on a biweekly to monthly basis for over a year. Most trees showed an early spring maximum in moisture content determined by TDR associated with leaf growth, and a late summer minimum in moisture content associated with the end of the dry season. Moisture contents ranged from 0.20 to 0.70 cm 3 cm −3 , with an annual percentage change in moisture of 15% to 70% depending on species and environmental conditions. A final field test was performed in northern New Mexico (U.S.A.) to examine the effect of trunk freezing on TDR measurements. This test confirmed that freezing conditions were recorded as a total loss of liquid water by the TDR method. These results suggest that further TDR calibration for wood, plus some understanding of the relation between tree moisture and physiological stress could be useful to several disciplines, ranging from irrigation scheduling to watershed management to forest ecology.

California↗

USGS1988

Air encapsulation during infiltration

A series of field and laboratory experiments were performed to measure the effects of air encapsulation within the soil's transmission zone upon several infiltration properties. In the field, infiltration rates were measured using a double-cap infiltrometer (DCI), and soil-water contents were measured using time-domain reflectometry (TDR). Before half of the infiltration experiments, CO 2 was injected through the DCI into the soil to reduce the amount of air encapsulation in the soil's transmission zone. For a gravelly loam as steady infiltration rates were approached, the average volumetric water content was 0.38 cm 3 cm −3 for control experiments and 0.43 cm 3 cm −3 for CO 2 experiments. The average steady infiltration rate was 0.42 cm min −1 for the control experiments compared to 4.40 cm min −1 for the CO 2 experiments. For a sandy loam as steady infiltration rates were approached, the average volumetric water content was 0.43 cm 3 cm −3 for control experiments compared with 0.45 cm 3 cm −3 for CO 2 experiments. The average final infiltration rate was 0.09 cm min −1 for the control experiments compared with 0.42 cm min −1 for the CO 2 experiments. In the laboratory, infiltration experiments were performed using repacked soil columns (15-cm i.d. by 140 cm long), again using TDR and CO 2 flooding. For a medium sand as steady infiltration rates were approached, the average volumetric water content was 0.29 cm 3 cm −3 for the control experiments and 0.36 cm 3 cm −3 for the CO 2 experiments. The average steady infiltration rate was 0.25 cm min −1 for the control experiments and 1.23 cm min −1 for the CO 2 experiments. For a loam as steady infiltration rates were approached, the average volumetric water content was 0.45 cm 3 cm −3 for the control experiments and 0.50 cm 3 cm −3 for the CO 2 experiments. The average steady infiltration rate was 0.02 cm min −1 for the control experiments and 0.10 cm min −1 for the CO 2 experiments. These results suggest that a significant portion of the total encapsulated air resided in interconnected pores within the soil's transmission zone. For the time scale considered, this residual air caused the effective hydraulic conductivity of the transmission zone to remain at a level no greater than 20% of the saturated hydraulic conductivity of the soil.

Soil Science Society of America Journal↗