Distribution and chemistry of manganese,iron, and suspended particulates in Orca Basin

The intense halocline and redoxcline in the Orca Basin, northwest Gulf of Mexico, induce dramatic water column profiles for manganese, iron, and suspended particulates. Within a 17 m interval, the salinity of the basin water increases from 66 to 260 & permil and dissolved oxygen decreases to zero. Midway through this transition zone, concentrations of suspended matter peak at 900 g/liter. Dissolved iron and manganese concentrations in the anoxic brine increase from oceanic values to maxima of 1.6 and 22 mg/liter, respectively. Upward migration of dissolved manganese from the brine leads to production of manganese-rich particles in the slightly oxygenated overlying water.     

Book reviews

VANISHING RAIN FORESTS: the ecological transition of Malaysia (Oxford Monographs on Biogeography No.5) by S.R. Aiken and C.H. Leigh. 19 × 25 cm, xvii and 194 pages. Clarendon Press, Oxford 1992. (ISBN 0 19 854242 9) $130.00 (hard)

ECOGEOGRAPHY AND RURAL MANAGEMENT: a contribution to the International Geosphere‐Biosphere Programme by J. Tricart and C. Kiewiet de Jonge. 267 pages. Longman/Wiley, New York 1992. (ISBN 0 582 06273 X) $51.00.

THE NEW SOCIAL ECONOMY: reworking the division of labor by A. Sayer and R. Walker. 15 × 23 cm, viii and 306 pages. Blackwell, Cambridge MA, 1992. (ISBN 1 55786 280 X) $49.95 (soft)

TROPICAL AFRICAN DEVELOPMENT: geographical perspectives edited by M.B. Gleave. 366 pages. Longmans/Wiley, New York 1992. (ISBN 0 582 30147 5)

MINING AND INDIGENOUS PEOPLES IN AUSTRALASIA edited by J. Connell and R. Howitt. 13 × 21 cm, × and 205 pages. Sydney University Press, Sydney 1991. (ISBN 0 424 00177 2) $22.95 (soft)

GOVERNMENT SCHOOLS OF NEW SOUTH 1848 TO 1993 (Fourth edition) edited by M. McPherson. 21 × 30 cm, 242 pp. NSW Department of School Education, Sydney, 1993. (ISBN 0 7310 0288 1). $22.00 (soft)(inc. postage).     

A modified light transmission visualization method for DNAPL saturation measurements in 2-D models

In this research, a light transmission visualization (LTV) method was used to quantify dense non-aqueous phase liquids (DNAPL) saturation in two-dimensional (2-D), two fluid phase systems. The method is an expansion of earlier LTV methods and takes into account both absorption and refraction light theories. Based on this method, DNAPL and water saturations can rapidly be obtained point wise across sand-packed 2-D flow chambers without the need to develop a calibration curve. A single point calibration step is, however, needed when dyed DNAPL is used to account for the change in the transmission factor at the dyed DNAPL–water interface. The method was applied to measure, for the first time, undyed DNAPL saturation in small 2-D chambers. Known amounts of DNAPL, modeled by tetrachloroethylene (PCE), were added to the chamber and these amounts were compared to results obtained by this LTV method. Strong correlation existed between results obtained based on this method and the known PCE amounts with an R² value of 0.993. Similar experiments conducted using dyed PCE showed a stronger correlation between results obtained by this LTV method and the known amounts of dyed PCE added to the chamber with an R² value of 0.999. The method was also used to measure dyed PCE saturation in a large 2-D model following sparging experiments. Results obtained from image analyses following each sparging event were compared to results obtained by two independent techniques, namely gas chromatography–mass spectrometry (GC/MS) analyses and carbon column extraction. There was a good agreement between the results obtained by this LTV method and those obtained by the two independent techniques when experiments were carried out under stable light source conditions and errors in mass balance were minor. The method presented here can be expanded to measure fluid contents in three fluid phase systems and provide a non-destructive, non-intrusive tool to investigate changes in DNAPL architecture and flow characteristics in laboratory experiments.     

Pyroclast textural variation as an indicator of eruption column steadiness in andesitic Plinian eruptions at Mt. Ruapehu

Hudson is one of the most active volcanoes in the Southern Andes—it had one of the largest eruptions of the 20th century in 1991 (VEI?=?5) and smaller eruptions in 1971 (VEI?=?3), maybe 1973, and 2011 (VEI of 1-2). We use satellite-based interferometric synthetic aperture radar (InSAR) and thermal imagery to characterize the activity of Hudson between 2004 and 2011 and during the 2011 eruption. InSAR data show that the volcano inflated between 2004 and 2010 with a maximum change rate of between 2 and 3 cm/yr—about half of the deformation rate observed during a previous deformation episode from 1993–1999. Inversion for an inflating point source suggests magma accumulation beneath the SW part of the caldera at an average depth of 10 km. This inferred source is deeper than both the sources estimated for the magma chamber of the 1991 eruption (from petrology) and for the 1993–1999 deformation event. Also, the deformation from 2004–2010 is centered at a slightly different location and has a smaller volume change than that between 1993–1999—further indicating that there is either a large magma reservoir or several separate ones. While the deformation center is a few km from the eruption location near the caldera rim, the two are possibly linked since the predicted static Coloumb stress changes due to the inferred inflation source would encourage unclamping on potential faults in the caldera rim. We also analize nighttime satellite thermal images from MODIS and ASTER. While MODIS did not show any unambiguous evidence for hot spots, ASTER thermal imagery show that at least four months before the eruption there were locations with temperatures 7–8ºK above background. Lahars observed by helicopter overflights on 4 March 2011 and October 2011 suggest that the hotspots may have been caused by lakes or subglacial melting. There is no InSAR data available for the months immediately preceding the eruption, but the ASTER thermal imagery results may indicate an increase in geothermal activity that could have been used to forecast the eruption.     

The Geospatial Semester: Concurrent Enrollment in Geospatial Technologies

Geospatial technologies are becoming more ubiquitous in our society; however, efforts to sustainably and effectively bring these tools to secondary education have proven challenging. An innovative program in Virginia, the geospatial semester (GSS), is described. The program offers high school students the opportunity to learn about geospatial technologies and apply them to local problems, and students can earn university credit. This article shares details of the program, along with examples of student work. Assessment of the program's impact shows that GSS students have increased spatial vocabularies and improved performance in making claims and providing evidence compared with non-GSS students.