The Neoglacial History of Mt. Thielsen, Southern Oregon Cascades

Abstract

Little Ice Age (LIA) deposits are recognized on Mt. Tbielsen, southern Oregon Cascades (43° 9' N, 122° 3' W), based on particle morphology and relative position. The initial advance, Lathrop 1, created a sharp-crested moraine and a protalus rampart within 200 m of the headwall. The retreat of the glacier and recent ice movement, Lathrop 2, is recognized by the deformation of the moraine and a mantle of "protalus till" creating a polygenetic "push-deformation'' moraine. Both the moraine and the protalus rampart have sparse vegetation, no lichens, and a lightly weathered Cox/C soil. This sequence is correlative with LIA Phase 1 and Phase 2 on Mt. Jefferson, central Oregon Cascades, and is broadly correlated with LIA deposits throughout the Cascades, Sierra Nevada, and Rocky Mountains. There is no evidence for pre-LIA deposits at Mt. Tbielsen. The ELA on Lathrop Glacier (2450 m) is lower than ELAs on nearby glaciers. The glacier probably exists because of its preferential topographic position and extensive debris cover; thus, if annual snowfall decreases the glacier will persist longer than a similar invaluable support from my dedicated field assistants JeffLafrenz, Wally Lafrenz, Pat

Spatial and morphological change of Eliot Glacier, Mount Hood, Oregon

“…and Nylen (2004), and as such south-facing glaciers will retreat more than larger glaciers. Other Oregon Cascade stratovolcanoes such as Mount Thielsen (Lafrenz, 2001) and Three Fingered Jack (O'Connor et al, 2001) have small remaining glaciers that are confined to north or northeast aspects, which have persisted because of originally larger sizes than their south-facing counterparts as well as headwall shading. (Lundstrom, 1992) insulates the ice and inhibits melt, and for thicknesses less than 2 cm, melt is accelerated.…”

“…Lillquist ( 1989) identified LIA moraines on Mount Hood and possibly moraines dating to approximately 4,500 -5,000 years ago . LIA moraines 7 have also been identified on Mount Jefferson (Scott, 1977), the Three Sisters (Marcott, 2005), Broken Top (Dethier, 1980;Marcott, 2005), and Mount Thielsen (Lafrenz, 2001). Other moraine sets downslope from the LIA moraines on the Three Sisters and Broken Top place glacial advances/stands at about 2,000 -3,000 and 4,500 -6,500 years ago .…”

A Tale of Three Sisters: Reconstructing the Holocene glacial history and paleoclimate record at Three Sisters Volcanoes, Oregon, United States

“…McLoughlin (Carver, 1972) and the Lathrop phase 1 and 2 moraines of Mt. Thielson (LaFrenz, 2001). In these local studies the moraine deposits lack Mazama tephra, have little to no soil development, are within 0 -300 m of modem glacier termini, and are well developed with sharp crests.…”

“…(Carver, 1972;Lafrenz, 2001;LilIquist, 1988;Scott, 1974;Scott et aI., 1990) and the western United States (Anderson and Anderson, 1981;Burrows et aI., 2000;Crandell, 1969;Madsen and Currey, 1979;Miller, 1969). Three Sisters occurred during the mid Holocene (2.5 -8.0 ka.…”

A Tale of Three Sisters: Reconstructing the Holocene glacial history and paleoclimate record at Three Sisters Volcanoes, Oregon, United States

“…and the lack of developed soil horizons and plant cover on the moraine slopes, the LIA advances at Three Sisters likely reached their maximum positions within the last 150-250 years, which is consistent with temperature depressions recorded in tree rings from Oregon and other land based temperature data (O'Connor et aI., 2001;Wiles et aI., 1996). The LIA deposits at Three Sisters and Broken Top are correlative in time with LIA moraine deposits in other regions of Oregon (Carver, 1972;Lafrenz, 2001;LilIquist, 1988;Scott, 1974;Scott et aI., 1990) and the western United States (Anderson and Anderson, 1981;Burrows et aI., 2000;Crandell, 1969;Madsen and Currey, 1979;Miller, 1969). (accumulation area ratio) lower than modern glaciers.…”