Leader: Nico M. Hauwert, Ph.D., Professional Geoscientist, Balcones Canyonland Preserve Program Manager
Trip Limit: 30 attendants
Note: There are opportunities to enter caves during this trip and helmets, headlights, and knee pads will be provided for safety and to reduce the risk of spreading white nose syndrome.
Focus: This field trip examines common reasons why most caves were filled across the area and provides tools for recognizing filled caves. A common misconception is that caves are found open and can readily be identified by a geologist trained in karst terranes. The reality is that caves were widespread filled for a variety of reasons that will be examined in this fieldtrip. Caves known today generally were excavated by cavers. Caves, especially when filled are generally not identified prior to development of sites, and are more likely discovered during construction or later catastrophic collapse. However, features that are highly likely to be caves can be identified by experienced cave stewards, through geophysics, surface contour maps, LIDAR and occasionally on aerial photographs. Where caves are filled actual discovery of caves and understanding its importance necessitates excavation. How historical practices affected recharge to aquifers, potential groundwater contamination, flooding, habitat for wildlife, education/recreational resources, historical records archived in cave deposits, and loss of heritage features for the public to experience. This trip will also examine sinkhole morphology and the geologic factors affecting cave development and cave density. This trip is dedicated in memory of Bill Russell, my mentor in finding caves and one with an amazing record for finding concealed caves.
9:00 am: leave Recreation Center
9:15 am examine Academy Cave that extends beneath Texas State University
10:30 am. Dahlstrom Ranch. Here we examine common ranching practices including trash filling of sinkholes, filling of caves to prevent damage to livestock, and plugging of sinkholes to create stockponds.
12:30 pm. Lunch. Box lunch provided.
1:00 pm. Onion Creek WQPL. Examine creek swallet caves on Onion Creek.
2:00 pm. Examine 80 feet deep Hoskins Hole shaft. This cave was partially filled with trash and restored.
2:30pm. Hudson WQPL. This former ranch was proposed for a 1,400 home development utilizing organized sewage system effluent infiltration. No caves were identified in the submitted geologic assessment. An 8-day assessment allowed by court order utilizing teams of cavers and geologists identified 140 significant features including 7 caves, 5 likely filled caves or sinkholes, and 3 large-internal drainage sinkholes. The site was acquired by the City of Austin for preservation. The field trip will examine several caves and other features on the site.
4:30 pm. Return to San Marcos.