About This Project

The Pinaleño Mountains in Arizona have an unusually flat summit. Why haven't streams carved it into rugged peaks? I hypothesize that streams lack the coarse sediment needed to erode farther uphill. I will test this by comparing new summit erosion rates with published rates from the steep sides, alongside my previous field and landscape analyses. Together, these findings could help scientists recognize how sediment shapes mountain landscapes, bridging theory and real-world observations.

Ask the Scientists

What is the context of this research?

The Pinaleño Mountains rise over 10,000 ft in southeastern Arizona's Basin and Range, with steep sides surrounding an unusually flat summit. Despite millions of years without mountain building (uplift), streams have not carved it into rugged peaks.

My fundamental question is: What surface process is keeping the summit of this mountain range so flat? Uplift, climate, and rock type alone cannot fully explain its shape. The answer may lie in the sediment carried by streams.

Coarse sediment acts like sandpaper, helping mountain streams grind into bedrock. Without enough coarse sediment, erosion is inhibited. I hypothesize that the summit supplies water but little coarse sediment, making it harder for streams below to carve farther uphill. To test this, I will collect sediment samples to measure long-term summit erosion rates and compare them with published rates from the steep sides. Much slower summit erosion would support my hypothesis and reinforce prior field observations.

What is the significance of this project?

The tools effect describes how coarse sediment helps rivers erode bedrock. Although studied in models and labs, its influence across mountain ranges is hard to identify. My analysis of digital elevation models (DEMs) revealed a promising clue: when I recalculated stream steepness without counting the flat summit's drainage area, the patterns more closely matched those expected for a landscape of this age. This suggests streams may receive water from the summit without enough sediment to erode efficiently.

But a pattern alone cannot confirm its cause. This project will provide the missing test: long-term summit erosion rates. Combined with prior field surveys and DEM analyses, these data will help determine whether sediment shortages can explain the flat summit.

This is significant because, if supported, the approach could give scientists a new way to recognize the tools effect in other mountain ranges, connecting theoretical predictions with real-world evidence.

What are the goals of the project?

The funds will cover lab fees and hands-on training at the University of Vermont's NSF-funded Community Cosmogenic Facility, including travel, lodging, and meals for two visits several months apart, as well as the remaining isotope measurement costs at Purdue's PRIME Lab.

Specifically, I will collect 10 sediment samples from small streams on the Pinaleños' summit. After sieving the samples at my institution, I will visit UVM's specialized clean laboratory, where researchers receive hands-on training in preparing samples for cosmogenic isotope analysis. With staff guidance, I will separate and purify quartz during my first visit and extract beryllium-10 during my second. I will then ship the prepared samples to Purdue for beryllium-10 measurement by accelerator mass spectrometry (AMS). This established method measures erosion over thousands of years and was also used for published measurements from the steep flanks, enabling a direct comparison.