Abstract

Undirhlíđar ridge on the Reykjanes Peninsula in southwest Iceland is a pillow-dominated glaciovolcanic tindar ridge. This project presents an analysis of vesiculated glassy pillow lava rinds from Undirhlíđar ridge as a method of understanding glacial ice thicknesses and behavior during the late Weichselian. Undirhlíđar ridge is bounded in the northeast and southwest by Undirhlíđar and Vatnsskarđ quarries, respectively. This study enlarges the emplacement pressure data set, previously restricted to the two quarries (Hiatt, 2014; Wallace, 2016), to now include observations and samples from the ~3 km area of the ridge that runs between the quarries. Emplacement pressures were calculated using geochemical analyses of glasses (EPMA) or whole-rocks (XRF), along with FTIR analysis of volatiles. Based on the distribution of emplacement pressures of 35 samples, a story can be developed that describes the interaction of volcanic activity and paleo-ice thicknesses during the construction of the ridge. The model that best explains the data includes multiple eruptions, ridge-wide changes in ice thickness, and local lake-level fluctuations. There was an initial eruption in which the bulk of the ridge was emplaced in a static lake. Near the end of the eruption, extensive melting of ice caused a fluctuating lake and variable drainage events, leading to along-axis variability and across-axis variability through differences in emplacement of core and flank pillow lavas. There was a time interval in which ice thickness conditions were able to reset to conditions similar to when the first eruption began. A second eruption took place in a lake that was relatively static, based on the small amount of samples analyzed from the second eruption. It is likely that most of the ridge emplaced during the second eruption eroded away. Actual emplacement pressures involve a complexity that accounts for along-axis variability across the ridge, core to flank variability, and age disparities, evidence that subglacial eruptions are far more complex than previously thought. The work of Pollock et al. (2014) demonstrated this through geochemistry, and paleo-water data only confirms and adds to that complexity.

Advisor

Judge, Shelley

Department

Geology

Publication Date

2017

Degree Granted

Bachelor of Arts

Document Type

Senior Independent Study Thesis

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© Copyright 2017 Chloe Wallace