By Max Cunningham
June 12, 2014
We continued to sample boulders in Valle de Las Morrenas, Valle Talari, where the hostel sits, and several places along Mount Chirripó’s ridgeline.
The view from the top of Mount Chirripó is spectacular. Looking out along the ridge I could see huge boulders of granodiorite produced by exfoliation, or the response of rock at the surface to the removal of ice.
The actual summit of Chirripó, however, is a very different kind of rock. I believe the peak is composed of a sedimentary rock that was melted and then fused back together as the magma that formed the granodiorite rocks moved toward the surface. This metamorphosed sandstone (meta-sandstone) is extremely hard, and resistant to weathering processes.
In the meta-sandstone near the summit of Mount Chirripó, I discovered glacial striations. These striations occur at 12,513 feet (the summit is 12,529 feet), which is a good 1,000 feet above the moraines in the upper portion of Valle de Las Morrenas.