Rock glaciers on the west slope of South Baldy, Magdalena Mountains, Socorro County, New Mexico
John W. Blagbrough and Brown, H. Gassaway, III
South Baldy is a prominent peak in the central portion of the Magdalena Range approximately 128 km southwest of Albuquerque and 28 km west of Socorro, New Mexico (fig. 1). Access is provided by U.S. Highway 60 and U.S. Forest Service Road 235 (Water Canyon Road). The junction of U.S. 60 and Water Canyon Road is approximately 17 km east of Magdalena and 24 km west of Socorro. From this junction the distance to the South Baldy area is 18 km. The six rock glaciers described in this paper are on the west flank of South Baldy and are accessible by foot from the mountain crest (fig. 2).
The Magdalena Mountains are a north-trending fault-block range some 40 km long and as much as 18 km wide. The range is bounded on the northeast by La Jencia Basin, on the south by a series of washes tributary to Rocky Arroyo, and on the west by the intermontane valley of Milligan Gulch. The Magdalena Mountains abruptly rise some 1285 m from a basal elevation of approximately 2000 m; their crest has an altitude of about 3000 m. South Baldy is the highest peak with a summit elevation of 3287 m.
The northern portion of the Magdalena Mountains, north of Water Canyon, consists of Precambrian igneous and metamorphic rocks over- lain on the crest and western slope by Paleozoic sedimentary rocks. Tertiary volcanic rocks overlie Paleozoic rocks in the northern part of the range and comprise all of the bedrock exposures south of Water Canyon, including South Baldy. The debris composing the rock glaciers is derived mainly from rhyolitic ash-flow tuffs.
Mass wasting is one of the dominant geomorphic processes operating in the Magdalena Mountains. Much of the exposed bedrock is intensely fractured by intersecting, steeply dipping joint sets. The closely spaced fractures allow surface water to penetrate the bedrock where it is subjected to repeated freeze-thaw cycles. The resultant ice wedging has produced extensive talus slopes throughout the mountains. Many of these slopes have undulating surfaces consisting of many small ridges and furrows. Ridges are parallel to the contour, indicating down slope movement which may be due to frost creep or solifluction. Soil slumps, solifluction lobes, and snow avalanche chutes also are common, especially at higher elevations.
The town of Magdalena, at an elevation of 1993 m, has the closest weather station maintaining continuous long-term weather records. Thirty- year normals for the period of 1941-1970 indicate a mean annual temperature of 11.3°C (U.S. Department of Commerce, 1973). January is the coldest month with a mean temperature of 0.9°C; July is the warmest month with a mean temperature of 22.1°C. For the same period the average annual precipitation was 26.44 cm, with 60 percent of the total occurring during the three months of July, August, and September. Interpretation of climatic data presented by Tuan, Everard, and Widdison (1969) indicates a vertical temperature gradient of — 0.9°C/100 m and a vertical precipitation gradient of + 3.49 cm/100 m for the Magdalena area. Utilizing these figures, the following crude approximations of the current climatic conditions were determined for the South Baldy area: mean annual temperature 0.2°C; mean January temperature — 10°C; mean July temperature 11°C; mean annual precipitation 76 cm; and mean total precipitation for July, August, and September 46 cm.
- Blagbrough, John W.; Brown, H. Gassaway, III, 1983, Rock glaciers on the west slope of South Baldy, Magdalena Mountains, Socorro County, New Mexico, in: Socorro region II, Chapin, C. E., New Mexico Geological Society, Guidebook, 34th Field Conference, pp. 299-302.