Student Research

Philip Chapman:

Iceland is battling a soil erosion problem throughout the country due to a lack of significant vegetation cover, steep terrain, high rainfall, and frequent volcanic activity. The goal of this study was to estimate Iceland’s soil erosion by calculating the revised universal soil loss equation (RUSLE) using a geographic information system (GIS). The results were compared to a 1998 field study of Iceland’s soil erosion by the Agricultural Research Institute of Iceland and the Icelandic Soil Conservation Service. Remote sensing data were used to derive estimates for spatially distributed soil loss equation factors. Of these factors, two—the conservation practice and soil erodibility—were held constant for the entire country and thus not used. The cover management factor was computed using a 1 kilometer resolution Greenland and Iceland land cover map from 2000 published by the European Commission Joint Research Centre. The rainfall erosivity factor was estimated using annual rainfall averages from 1971-1993 that were obtained from the Icelandic Meteorology Office. These points were encoded onto a map of Iceland and projected into contours. The slope steepness and slope length factors were estimated using a digital elevation model (DEM) from the ETOPO2 Global 2’ Elevation data set. The cover management, rainfall erosivity, and topography factors were converted to a raster projection so that maximum RUSLE factors could be calculated to display predicted areas of high erosion. The individual RUSLE factor predictions were overlain to predict Iceland’s areas of maximum potential soil erosion. When compared to published field data, the GIS- generated RUSLE underpredicted the observed soil erosion for Iceland, indicating that the maximum factor combination is not driving soil erosion in Iceland. It appears that the land cover of Iceland is driving the soil erosion because the maximum potential soil erosion map for land cover appears to correlate well with the observed soil erosion.  This project was supervised by Dr. Kathy Licht, with help from Dr. Jeff Wilson.

Tamara McPeek:

The formation of soil from the weathering of rocks is a dynamic process, affected by rock characteristics, climate, biogenic activity, and time. The purpose of this project is to use biogeochemical analyses to determine the interplay between biogenic activity and soil formation in historically dated basalts with nearly identical geochemical compositions in southern Iceland.

Soil samples were taken from lava flows of four ages: 934 AD, 1300 AD, 1554 AD, and 1783 AD. Initial analyses have focused on the ingrowth of organic matter as a function of time in these young soils, an important factor in determining carbon uptake and sequestration during the weathering of volcanic rocks. We found an increase in the organic matter content with age of flow, reflecting the activity of surface plants and the ingrowth of soil microbial biomass. The soil derived from the 934 AD flow had an average of 3.3 kgC/m2 and the soil derived from the 1783 AD flow had an average of 0.20kgC/m2, which is within the range of carbon content range from 0.1 to 21.6 kgC/m2 found in the rocky and tundra environments. The average carbon uptake in these soils was 1–3 gC/m2/yr, which are comparable to 0.2-2.4gC/m2/yr for tundras. Ongoing analyses will include SEM (Scanning Electron Microscope), microprobe, and phosphorus and nitrogen analyses. These tests will target the surface geochemical evidence of mineral weathering during soil formation, as well as potential changes in the storage of key nutrients, phosphorus and nitrogen, with time. This research will eventually provide insight into the impact of biogenic activity on the weathering of rocks and subsequent soil formation, and the rate at which these processes occur.
 

Kenny Brown, Nicole Fohey, and Christy Carter:

This study aims to examine the genetic relationship between felsic and voluminous basaltic lavas in mid-ocean ridge settings. Salton Sea rhyolites erupted through sediments blanketing the intersection of the East Pacific Rise and the San Andreas fault zone. The Torfajökull volcanic complex is located near the Mid-Atlantic Ridge, at the intersection of the active East Rift Zone and the Southeastern Zone. Chemical analyses reveal that the samples include trachydacite and rhyolite. Torfajökull samples have 63-71% wt. silica, high amounts of alumina (13-15% wt.) and low phosphorous (<0.1% wt.) and Sr (80-120 ppm). Salton Sea rhyolite is comparatively silica rich (74%), has lower alumina and Sr, and higher K/Na. Loss on ignition to 700C indicates that all trachydacites and rhyolites contain <0.5% wt. H2O.

The Salton Sea rhyolite is a series of five small domes. Zircon Th-U ages are ~17 ka, identical to a ~16 ka K-Ar whole rock eruption age (Muffler and White, 1969). Inherited zircons of Jurassic age suggest this rhyolite represents small volume partial melts of Jurassic granitic basement, or deltaic sediments derived from Jurassic basement rocks exposed on the northeastern shoulder of the Salton trough.

Torfajökull is host to several subglacial and postglacial (<10 ka) rhyolite eruptions; we focused on three postglacial flows from the Domadalshraun vent, which erupted trachydacite and rhyolite between 8 and 2 ka (McGarvie, 1985). Th-U ages of zircon from two samples are 22-60 ka, ~20-50 ka older than eruption ages; the earliest flow has relatively older zircons. The earliest flow is more homogeneous, felsic, and has An4-7 feldspar phenocrysts and matrix grains, whereas later flows are more heterogeneous, mafic, have An7-20 plagioclase phenocrysts, and include more abundant xenocrysts (An30-70) and mafic to intermediate inclusions. These observations suggest that the flows erupted from a thermally and compositionally zoned Domadalshraun magma chamber formed at least 60 ka.