Cordilleran Section - 115th Annual Meeting - 2019

Paper No. 11-18
Presentation Time: 9:00 AM-6:00 PM


NUNEZ, Yasiri1, THEISSEN, Kevin M.2, THOLE, Jeff3, SWANSON, Reid1, HENSLEY, Adam1 and THOMPSON, Tori2, (1)Geology, University of St. Thomas, 7708 beard ave N, Brooklyn Park, MN 55443, (2)Geology, University of St. Thomas, Mail# OWS 153, 2115 Summit Ave, Saint Paul, MN 55105, (3)Geology Department, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105

We have tentatively identified the source and age of two tephra layers in a 274 cm long core collected from Lake Myvatn in northern Iceland using a Scanning Electron Microscope with Energy Dispersive Spectroscopy (SEM-EDS). Here we report these findings and further results of our ongoing analysis of tephra layers in the core. Some of the larger tephra layers are likely from eruptions such as 1477 or 1717 Veidivotn. Previous analysis of tephrochronology in the Lake Myvatn core was done the summer of 2018 where a distinctive felsic tephra layer was chemically analyzed using the SEM-EDS. After compiling the data from the SEM, the chemical properties of the tephra was cross-analyzed using published data found on Tephrabase. Published data was also used to confirm the likelyhood of a potential match. As a result of the summer research, the Hekla 1104 eruption was identified due to its distinctive felsic composition. Further research continued fall of 2018 where three more tephra layers were examined. The same methodology was used to collect the chemical data where an average of 30 volcanic glass shard were analyzed under the SEM-EDS and then cross analyzed with data found on Tephrabase. The Simulation Manager (SIMAN) was also used in order to assesses the likeliness of a chemical match. From the fall research only one layer was identified to be the Katla 1416 eruption based on its SIMAN coefficient of 0.9498 which indicates a 94.5 % chemical match. The other two layers were left as unknown due to their range in chemical properties which place them between two different major volcanic systems in the region. This may be due to reworking of the tephra from erosion, biological disturbance or varying water levels present in the lake. Ongoing research will continue in the spring of 2019 to identify the two unknown layers and other potential tephra layers along the core. This ongoing research includes but it is not limited to further SEM-EDS analysis as well as using the minor elements present in both sections to find elemental matches.