Geomorphology

Stream channel response to urbanization in the humid tropical region of NE Puerto Rico

Project Description: 

Key science question:
• How does stream channel morphology respond to the addition of impervious cover in a humid tropical region adjusted to frequent large storms?

Research Location: 
Core Area(s) and/or Keywords: 

Geomorphology, Urbanization, Streams

Quantifying Hydrograph Unsteadiness and Sediment Cobble Dispersion

Project Description: 

Sediment transport is an intrinsically stochastic process, and measurement of bed load in the environment is further complicated by the unsteady nature of river flooding. Here we present a methodology for analyzing sediment tracer data with unsteady forcing. We define a dimensionless impulse by integrating the cumulative excess shear velocity for the duration of measurement, normalized by grain size. We analyze the dispersion of a plume of cobble tracers in a very flashy stream over two years.

Research Location: 
Core Area(s) and/or Keywords: 

Sediment Transport, Geomorphology, Hydrograph

Relevant Tools, Models or Publication Downloads: 

Longitudinal Patterns in Stream Channel Geomorphology and Aquatic Habitat in the Luquillo Mountains of Puerto Rico

Project Description: 

The hydrologic, geomorphic, and ecological dynamics of tropical montane
streams are poorly understood in comparison to many temperate and/or alluvial rivers.
Yet as the threat to tropical freshwater environments increases, information on the
dynamics of relatively pristine streams is important for understanding landscape
evolution, managing and conserving natural resources, and implementing stream
restoration. This dissertation characterizes the geomorphology and hydrology of five

Research Location: 
Relevant Tools, Models or Publication Downloads: 
Data Sets: 

Long-term landscape evolution of the Luquillo Mountains and its effects on today’s variability in erosion rates.

Project Description: 

Key Science Questions Involved:
1 – Large scale: When where the Luquillo Mountains uplifted to their present height?
2 – Mesoscale: The last 500-600 m of uplift generated a conspicuous wave of erosion still propagating toward the mountain tops. What is the magnitude of the spatial variability in erosion rate associated with this wave?

Core Area(s) and/or Keywords: 

Geormophology

Relative importance of sediment abrasion in downstream fining of grains and production of fine sediment.

Project Description: 

Key Science Questions Involved:
1. What is the relative importance of abrasion versus selective transport in causing downstream fining of river sediments?
2. What is the fraction of fine material that is produced by abrasion of gravel?

Core Area(s) and/or Keywords: 

sediment transport, abrasion, lithology, downstream fining

Relevant Tools, Models or Publication Downloads: 

Determining the Provenance of Suspended Sediment: Storm Sampling in Northeastern Puerto Rico

Project Description: 

Motivation for study:
1. How does a single precipitation event erode a landscape?
2. Can we determine provenance of suspended sediments during a flood event?
3. Do source areas contributing suspended sediments vary over the course of a hydrograph?

Research Location: 
Core Area(s) and/or Keywords: 

hydrograph, erosion, suspended sediment, isotopic fingerprinting

Weathering Processes on Landslides

Project Description: 

A landslide chronosequence will be instrumented (nested suction lysimeters for collecting soil/saprolite pore waters, rain collectors, runoff collectors) and analyzed (via a suite of geochemical analyses of both solid and aqueous samples) to study the effects of landslides on chemical weathering processes and rates, the spatial and temporal variability of chemical weathering profiles in the LCZO, and to explore hypotheses regarding the establishment and maintenance of steady-state regolith profiles.

Research Location: 

Modelling of soils in Luquillo Mountains

Project Description: 

Sue Brantley, Heather Buss, Katya Bazilevskaya, Lixin Jin

A reactive transport code will be used to model regolith development on one or more of the three relevant lithologies. The model will include flow, diffusion, and chemical reaction.

Research Location: 

Weathering of a chronosequence of landslides

Project Description: 

Sue Brantley, Heather Buss

We will analyze soils on five landslides that constitute a chronosequence of landslide events. These soils were sampled by Art Johnson as published in Zarin et al. (xxx): we will analyze the same samples for chemistry and mineralogy with respect to depth. We will also revisit these same landslides to resample and reanalyze. The goal is to understand how landslides affect weathering and solute fluxes in the Luquillo mountains.

Hornfels Weathering

Project Description: 

Sue Brantley, Heather Buss, Tim White

Regolith development on volcaniclastics metamorphosed to hornfels facies will be investigated. We will sample and analyze chemistry and mineralogy of soils and regolith down to bedrock as a function of elevation from the East Peak-West Peak ridge down to the unmetamorphosed sediments in the Icacos watershed along a catena. We will also measure corestone size along the catena. The goal is to understand the chemical weathering of the hornfels and how it differs from the unmetamorphosed volcaniclastics.

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