Bedrock Properties Influence Stream Channel and Landscape Form in the Guadalupe Mountains, New Mexico, USA
Abstract
We explore how rock properties and channel morphology vary with rock type in the Guadalupe Mountains. The rocks here are primarily composed of horizontally interbedded dolomite and quartz bearing layers. We focus on upstream sections of the network, where the channels have a relatively lower normalized channel steepness index (ksn) upstream and transition to higher ksn just downstream. We hypothesize that the high ksn reaches are mostly composed of relatively less fractured rocks and have fewer bedding planes than bedrock in the upstream low ksn reaches. Additionally, we hypothesize that exposed massive bedrock on hillslopes surrounding the high ksn reaches contributes to further steepening of channel slopes by supplying relatively large colluvial sediments which armor the less massive rock units. We use field observations, rock property measurements, and DEM analyses to test these hypotheses. Discontinuity intensity (length of fractures and bedding planes per unit area) was measured using FracPaq software to analyze traces of fractures on orthomosaics generated using Agisoft Photoscan. XRD and carbonate dissolution are employed to identify bedrock minerology where we collected Schmidt hammer measurements and discontinuity intensity data. ksn is calculated in channels and surrounding hillslope angles are measured using a 10 m DEM. Finally, we use PRISM climate data to explore if weathering has an impact on rock strength measurements. We find that: 1) high ksn reaches have rocks with higher discontinuity intensity than low ksn reaches; 2) there is more exposed massive dolomitic bedrock in the high ksn reaches; 3) the high ksn reaches are armored with larger boulders than the low ksn reaches; and 4) wetter parts of the landscape have rocks with lower Schmidt hammer values (holding ksn and mineralogy constant). From these results, we interpret the landscape to be in a stable configuration with base level for the upstream low ksn, reaches pinned by the relatively less erodible conditions downstream. Results from this study will help reconcile our understanding of the effect that rock properties have on stream channel form.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP31C2280A
- Keywords:
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- 1815 Erosion;
- HYDROLOGY;
- 1824 Geomorphology: general;
- HYDROLOGY;
- 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS;
- 8177 Tectonics and climatic interactions;
- TECTONOPHYSICS