Garth Ornelas

Years participated in RESESS: 2015, 2014, 2013

An Overview

Major: Physics

Academic Affiliation: Southwestern University


At a young age my obsession with the physical phenomena of our world spurred an interest in the outdoors and the pursuit of scientific knowledge. This same path led me to pursue an undergraduate degree in physics in order to gain a broad understanding of our universe so as to discover a more specific field of study to pursue in graduate school. My research at RESESS used a large centrifuge to study the hydraulic properties of an unsaturated silt layer. The centrifuge served as a catalyst in the water drainage process and provided data about the soil water retention curve in a matter of days as opposed to the months it would take using traditional methods.


2013- Centrifuge modeling of water infiltration and drainage in unsaturated silt layers

This study involves an analysis of water drainage from an initially saturated silt layer in a centrifuge permeameter to evaluate the hydraulic properties of the soil layer in unsaturated conditions up to the point where the water phase becomes discontinuous. These properties include the soil water retention curve (SWRC) and the hydraulic conductivity function (HCF). The hydraulic properties of unsaturated silt are used in soil-atmosphere interaction models that take into account the role of infiltration and evaporation of water from soils due to atmospheric interaction. These models are often applied in slope stability analyses, landfill cover design, aquifer recharge analyses, and agricultural engineering. The hydraulic properties are also relevant to recent research concerning geothermal heating and cooling, as they can be used to assess the insulating effects of soil around underground heat exchangers. This study employs a high-speed geotechnical centrifuge to increase the self-weight of a compacted silt specimen atop a filter plate. Under a centrifuge acceleration of N times earth’s gravity, the concept of geometric similitude indicates that the water flow process in a small-scale soil layer will be similar to those in a soil layer in the field that is N times thicker. The centrifuge acceleration also results in an increase in the hydraulic gradient across the silt specimen, which causes water to flow out of the pores following Darcy’s law. The drainage test was performed until the rate of liquid water flow out of the soil layer slowed to a negligible level, which corresponds to the transition point at which further water flow can only occur due to water vapor diffusion following Fick’s law. The data from the drainage test in the centrifuge were used to determine the SWRC and HCF at different depths in the silt specimen, which compared well with similar properties, defined using other laboratory tests. The transition point at which liquid water flow stopped (and Darcy’s law is no longer valid) was at a relatively high degree of saturation of 0.8. This finding is important as many water flow analyses in the literature assume that Darcy’s law is valid over a much wider range of degrees of saturation, an error that potentially may lead to overestimates of water flow in unsaturated soil layers.

2014- Monitoring Glacier Velocities in the Russian High Arctic

The 2200 km3 Academy of Sciences ice cap, located on Komsomolets Island in the Severnaya Zemlya Archipelago, is the largest ice cap by volume in the Russian High Arctic (Dowdeswell et al., 2002). We examine recent velocities variations at the outlet glaciers around the perimeter of the ice cap. Most of these glaciers are tidewater glaciers that calve into the ocean. Our observations of velocities at the five major outlet glaciers made between 2011 and 2013 are compared to the rates motions measured in the 1990’s and 2000’s (Moholdt et al., 2012; Stewart, 2014) to determine if the velocities have changed.

We implement a normalized cross-correlation pixel tracking process in order to determine the velocity of the ice stream-like outlet glaciers. Orthorectified high-resolution satellite image pairs from Worldview 1 and 2 with an ideal time separation of 1-3 months during the spring and summer are used. We select imagery from the spring and summer periods where crevasses are clearly observed. We estimate uncertainties by examining apparent motion at bedrock outcrops adjacent to the glaciers.

We find our velocities to be consistent with other research in the area for the timespan of 2009-2012 (Stewart, 2014), and see increases in velocity compared to results dating back to 1995 (Moholdt et al.). Our results also yield visible seasonal variations in velocity.

2015- Updating Tree Ring Width Chronologies of Engelmann Spruce in Subalpine Forests of Colorado’s Front Range

The effects of climate change on forests throughout the western United States have manifested in different ways including the outbreak of bark beetle infestations (Bentz 2010) and an increase in forest fire susceptibility caused by warming temperatures and drought in certain areas (Westerling et al. 2006; Sherriff et al. 2014).  We explore the direct correlations among climate variability and radial tree growth in recent years. We accomplish this by creating a tree ring chronology for a xeric and a mesic site on Niwot Ridge and then comparing the chronologies to past measurements taken in the 1980s by Villalba et al. (1994).

We looked for trees used to compile the past chronology and then cored samples from each site using an increment borer.  The samples were then mounted, sanded, and measured.  From these measurements we created stand-level chronologies and compared the trends to climate data in the area.

Comparison of these newly created tree-ring chronologies with the published chronologies based on sampling conducted in the 1980s indicates that the new chronologies were accurately created.  Based on the new chronologies extending through 2015, we discovered that at both a xeric and a mesic site radial growth is negatively correlated (i.e. growth is reduced) during warmer years and especially when the growing season one year prior to the formation of the annual ring is warmer.  The negative influence of warmer growing season temperatures on tree growth appears to be greater at the xeric site than at the mesic site.   Overall, these results imply that warming temperatures are likely to have a negative influence on tree growth rates in these high elevation stands.


Centrifuge modeling of water infiltration and drainage in unsaturated silt layers

Monitoring Glacier Velocities in the Russian High Arctic

Updating Tree Ring Width Chronologies of Engelmann Spruce in Subalpine Forests of Colorado’s Front Range