Assessing How The Rock Type Controls the Concentration of Incising Bedrock Gullies in the Gabilan Mesa

Assessing How Rock Type Controls the Concentration of Incising Bedrock Gullies In the Gabilan Mesa

Miguel FriasFaculty Advisor: George Hilley, Ph.D.

Mentor: Sam JohnstoneDepartment of Geological and Earth Sciences

Stanford University

SURGE Symposium – Aug. 13th, 2015

What controls the sensitivity of landscapes?

What controls the sensitivity of landscapes?

What controls the sensitivity of landscapes?

What controls the sensitivity of landscapes?

Gabilan Mesa primarily mud-rich rocks

Majority of area underlain by the Pancho Rico Formation

• Shallow marine• Mud rich

Formation Rock Type

Paso Robles -Conglomerate-Strong, well

cemented

Pancho Rico -Mud Clay Rich-Marine

Gabilan Mesa

6Introduction Objective Hypothesis Methods/Results Conclusion

Introduction Interest Hypothesis Methods/Results Conclusion

Slaking of core samples after one wetting and drying cycle

Before After

Gullies formed from headward retreat

9Introduction Interest Hypothesis Methods/Results Conclusion

Why are we interested?

• How do landscapes respond to changing climatic and tectonic conditions?

• Are landscapes over mud rich rock more vulnerable to erosion than other regions?

10Introduction Objective Hypothesis Methods/Results Conclusion

Are gullies more concentrated in mudstones than sandstones and conglomerates?

Introduction Objective Hypothesis ConclusionMethods/Results

Concentration of gullies within Gabilan Mesa is highly variable

12Introduction Objective Hypothesis Methods/Results Conclusion

Gullies are more frequent in Pancho Rico than Paso Robles

13Introduction Objective Hypothesis Methods/Results Conclusion

14Introduction Objective Hypothesis Methods/Results Conclusion

Is a basin more Pancho Rico or more Paso Robles?

15Introduction Objective Hypothesis Methods/Results Conclusion

Is a basin more Pancho Rico or more Paso Robles?

16Introduction Objective Hypothesis Methods/Results Conclusion

Is a basin more Pancho Rico or more Paso Robles?

Gullies are more frequent in Pancho Rico than Paso Robles

17Introduction Objective Hypothesis Methods/Results Conclusion

Deformation of Paso Robles can possibly provide information about relative uplift

18Introduction Objective Hypothesis Methods/Results Conclusion

Conclusion

Introduction Objective Hypothesis Methods/Results

• Rock type controls the density of gullies in the Gabilan Mesa

• Gully density within Pancho Rico formation much more variable than the Paso Robles

• Deformation of the local bedrock can provide information about relative uplift but need to reconsidered some of the mapped gullies

Conclusion

Acknowledgements

• Dr. George Hilley • Sam Johnstone• SURGE Program• Stanford University

Questions?