Mapping Ice Buried by the 1875 and 1961 Tephra of Askja Volcano, Northern Iceland Using Ground‐Penetrating Radar: Implications for Askja Caldera as a Geophysical Testbed for In Situ Resource Utilization

Abstract

AbstractEruptions of the Askja Volcano in Northern Iceland in 1875 and 1961 blanketed the caldera with rhyolitic and basaltic tephra deposits, respectively, which preserved layers of seasonal snowpack as massive ice. Askja serves as an operational and geophysical analog to test ground‐penetrating radar field and analysis techniques for in situ resource utilization objectives relevant to the martian and lunar environments. We conducted ground‐penetrating radar surveys at center frequencies of 200, 400, and 900 MHz to map the thickness and extent of tephra deposits and underlying massive ice at three caldera sites. We identified up to 1 m of tephra preserving up to 4.4 m of massive ice. We measured the real dielectric permittivity of the overlying tephra and the total attenuation at each frequency of the tephra and ice. A key objective of our investigation was to determine if attenuation (or loss) could be used as an additional diagnostic signature of massive ice preserved at depth when compared to ice‐free stratigraphy. Loss rates of the ice‐rich subsurface decrease with increasing ice thickness relative to the overburden, which may constitute a possible signature. Attenuation also increased with increasing frequency. The tephra, ice, and other volcanic deposits at each of our three caldera sites and the ice‐free, pumice‐mantled 1961 Vikrahraun lava flow exhibited consistently low loss rates at all frequencies. This result highlights the ambiguity associated with identifying the unique signature of ice within low‐loss stratigraphies, a possible challenge for its identification in the martian or lunar subsurface using radar.