STRUCTURAL ANALYSIS OF TENSILE FRACTURE SETS IN THE MEDICINE LAKE DACITE LAVA, CALIFORNIA

We present a preliminary structural analysis of tensile fracture sets in the upper surface of the Medicine Lake dacitic lava, Medicine Lake volcano, northern California. Using Google Earth and orthorectified drone images, we have analyzed ~1,000 tensile fractures across the entire lava to produce a representative data-set. We have measured the lengths and orientations of major fractures and used drone image-derived 3D models and DEMs to estimate fracture depth and fracture surface curvature. Previous studies documented the orientations of small numbers fractures in the Medicine Lake dacite, but did not integrate their formation with the emplacement of the lava. On-going research into silicic lava flow emplacement emphasizes the importance of tensile fracturing during emplacement and the extreme unlikeliness that silicic lavas will fold: this contradicts the existing literature that interprets many upper surface structures as ductile and compressional (i.e. folds). It is, therefore, important to understand the structural context of undisputed fracture sets to assess how and when they formed.