Rachel Medina

Rachel Medina

Years participated in RESESS:

An Overview

Major: Geology; Minors in Mathematics and Physics
Academic Affiliation: Fort Lewis College, Durango, Colorado
Research Mentors: Glen Mattioli, UNAVCO and John Braun, COSMIC
Computer Mentor: John Braun, UCAR
Writing Mentor: Lon Abbott, CU
Grad Student Mentor: Erin Leckey, CU


Rachel grew up in Longmont, Colorado and currently attends Fort Lewis College in Durango, Colorado. She is the student president of the Fort Lewis chapter of Engineers WIthout Borders. She has always been fascinated by the Earth, especially the mountains, and was inspired by a passionate instructor at Front Range Community College, where she took her first Geology course. She enjoys rock climbing, rafting, hiking, and backpacking.


An analysis of GPS and remote sensing data of Soufrière Hills Volcano, Montserrat, during the July 2003 dome collapse: Implications for detection of ash plumes and vertical deformation

A 210Mm3 dome collapse of the Soufrière Hills Volcano occurred on July 12th, 2003. Five continuous GPS receivers collected data at 30 sec intervals covering the massive collapse. One GPS station, HERM, located 1.6km northeast of the dome and volcanic vent, recorded a maximum vertical displacement of 1.98m from its mean elevation of 437m above sea level, with negligible horizontal movement. This large displacement was recorded during the peak dome collapse event when ash venting and a significant plume were most prominent. Both HERM and another station, SOUF, are in close proximity to the path of the pyroclastic flows resulting from the collapse. The SOUF site shows a maximum vertical displacement over the same time of only 0.43 m. GEOS satellite imagery from the event were examined and correlated with the apparent vertical displacement from HERM to test the relative contributions of: 1) the dome collapse and possible elastic crustal response to unloading and 2) tropospheric interference from co-collapse ash plumes. GOES infrared imagery was used to verify the temporal and spatial progression of ash and cloud cover by extracting gray scale values ranging from 0 to 255 for specific pixels proximal to the location of each GPS station. We observed no variation between gray scale values in the GEOS infrared band for specific pixels centered on the GPS sites. In addition, the GPS-derived zenith-wet-delay from HERM shows a decrease during the peak dome collapse when the plume was at its maximum intensity, which is not consistent with a substantial contribution from a volcanic plume. Accordingly, we infer that moisture content associated with the plume cannot solely account for the apparent vertical displacement of 1.98m observed at the HERM site and that some significant portion of the displacement is related to actual crustal motion during the collapse event.