Geologist, inventor, rock climber, and owner and CEO of Brunton, Lauren Heerschap will share the geology of her favorite rock climbing spots at an upcoming AAPG Women's Network Event. Today, we give you a preview.
The AAPG Women’s Network and the Midwest GeoSciences Group are hosting an upcoming free webinar, The Geology of Rock Climbing, on April 11 at 3pm CT. The presentation will be led by geologist, inventor, rock climber, and owner and CEO of Brunton International, Lauren Heerschap. You can sign up to attend here.
In anticipation of her presentation, we’ll visit two rock climbing locales she plans to highlight.🧗♀
You can read about one more rock climbing hot spot, Smith Rock in Oregon, in the latest edition of Explorer. Now, let’s get climbing!
Sharon Lyon
Editor, GeoLifestyle
The Shawangunk Ridge, New York
Vonnahmed1/Shutterstock.com
The Shawangunk Ridge is a long crest of resistant rock within the Appalachian Mountains that marks the western and northern edges of the Great Appalachian Valley.
About the ridge: Names change across state lines, but the formation extends from Virginia to New York, where it was named Shawangunk after a Dutch translation of a Native American word meaning ‘in the smoky air.’
The ridge is 7.5 miles at its widest, with a maximum elevation of 2,289 feet. It rises above a broad plain stretching to the Hudson River to the east. On the west are the low foothills of the Appalachian Mountains.
Geology: The ridge is topped by the Silurian-age Shawangunk Conglomerate, a hard, silica-cemented conglomerate and sandstone. It lies unconformably above the Ordovician Martinsburg Shale, a gray, deep marine/turbidite deposit.
During the preceding Ordovician period, mountains uplifted to the east during the Taconic Orogeny.
As the mountains eroded in the Silurian, 420 million years ago, a great braided stream/deltaic system flowed westward, carrying detritus into what is now Pennsylvania, Ohio, New York, and West Virginia.
The Shawangunk Conglomerate formed as part of this extensive sedimentary deposit, known as the Queenston Clastic Wedge. It is estimated that more than 150,000 cubic miles of rock in the Taconic ranges were eroded to produce the wedge.
During the Alleghenian Orogeny in the Permian, 270 million years ago, the sedimentary rocks were uplifted and deformed in the continental collision that formed Pangea.
Erosion truncated the rock layers along the eastern margin of Shawangunk Ridge. The durability of the conglomerate and sandstone resulted in the prominent cliffs seen today.
Advancing glaciers scoured the ridges during the Pleistocene, leaving pockets of till and fans of talus.
Climbing: The Gunks (short for Shawangunks) is one of the premier climbing areas in the country with some of the best easy and moderate traditional climbs (lead climbing with removable ropes and bolts). The rock has horizontal cracks. I’m interested in learning from Lauren how this affects the climb.
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Devils Tower is located on the west flank of the Black Hills in Wyoming. The tower rises 867 feet from its base and is known for its columnar jointing. Because of its striking visage, Teddy Roosevelt established the Devils Tower National Monument in 1906.
Geology: The oldest rocks in the Monument area are Triassic and Jurassic marine and beach deposits—sandstones, limestones, and gypsum beds.
Approximately 50 million years ago, as the Rocky Mountains and the Black Hills were uplifted, magma intruded into these sedimentary rock layers. Cooling of the magma formed a phonolite porphyry, an intermediate to silicic intrusive igneous rock with a fine-grained gray groundmass surrounding larger crystals of white anorthoclase feldspar and dark-green pyroxene.
The origin of Devils Tower has been variously postulated to be a stock, a laccolith, a volcanic neck, or a maar-diatreme volcano. However, the lack of extrusive rock or pyroclastic material in the vicinity and the uniform composition and grain size of the phonolite discount the origin of a volcanic neck or plug.
The total stratigraphic section at the time of intrusion is estimated to have been 7,000 feet above the present level of Devils Tower. Between 5 and 10 million years ago, erosive forces began to expose the surface of Devils Tower.
Devils Tower’s columnar jointing is one of the largest and most spectacular examples of this phenomenon. As the molten rock cooled, it contracted, forming hexagonal shapes. Many of the tower’s columns are irregular or pentagonal, possibly due to their large size.
A study of the joint angles, which relate to the thermal gradient, indicates that the magma body forming the original intrusion was probably teardrop-shape with the smaller end downward.
Erosion has formed a large boulder field at the tower’s base, with massive rocks strewn over a 13-acre area. Small pieces of rock, the size of baseballs or basketballs, fall regularly.
Climbing: Hundreds of parallel cracks make Devils Tower one of the finest crack climbing areas in North America (This is when climbers use a method called jamming, in which they position their hand in the cracks to better utilize the cracks as holds). Lauren will share more about her experiences at Devils Tower during the webinar.
Fun fact: In the 1977 classic film “Close Encounters of the Third Kind,” Richard Dreyfuss has a vision of Devils Tower after an alien encounter. Trying to figure out its meaning, he makes multiple models of the tower.
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