118 Geomorphology (Posters)

FOREST FIRE-ENHANCED MODIFICATION OF CLAY MINERALS IN SOILS IN AND AROUND THE HAYMAN (2002), COLORADO, BURN

Paper number: 118-17
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

High intensity forest fires can alter the clay minerals found in soils. These minerals can be degraded, collapsed, as well as completely destroyed. Signatures of these fires may remain for years after the burns. To ascertain the impact of high intensity fire on soil physical properties, samples were collected from the area in and around the 2002 Hayman, Colorado, fire. These included burned samples from several areas within the perimeter of the fire (taken one to four months following the fire), unburned samples near the origin of the fire, as well as samples from areas of historic burns nearby. This series of samples show not only the immediate implications of high intensity forest fires on soil-clay mineralogy, but also the recovery over time of these minerals. Identification of the clay minerals was done using X-ray diffraction of the 5 to 30° 2q range of oriented clay mineral fractions. A series of XRD spectra were obtained for each sample, including air-dried, ethylene glycol saturated, and furnace heated to 400° and 550°C.

The unburned samples contain mixtures of illite, mixed layer illite/smectite and illite/vermiculite, kaolin, mixed layer chlorite, as well as clay-sized quartz, plagioclase and K-feldspar. At depths close to the surface (to 7.7 cm), illite, mixed layer illite/smectite, and kaolin are present. At depths to 13 cm, mixed layer illite/vermiculite as well as clay-sized quartz and plagioclase appear in addition to those found at shallower depths. Eventually (at depths to 27 cm) mixed layer illite/smectite and illite/vermiculite disappear and mixed layer chlorite as well as clay-sized K-feldspar appears.

The recently and historically burned samples will be compared to the unburned samples in order to determine the effects of the fire on these minerals. Intensities as well as shifts in the d(001) spacings will also be compared to determine changes in relative amounts of the individual clay minerals as well as effects on their structure.