THE BLUE DIAMOND LANDSLIDE: EVIDENCE OF A MULTI-PHASE EMPLACEMENT FOR A LARGE-SCALE LANDSLIDE

Remnants of the Blue Diamond landslide breccia are exposed throughout the foothills of the eastern Spring Mountains near Blue Diamond, Nevada. Uncertainties surrounding the origin and emplacement of the of the ancestral landslide have emerged based on the disparate distribution of landslide outcrops. This study uses detailed sedimentological data and observations to interpret a two-phase emplacement history for the Blue Diamond landslide.

Sedimentological observations of a discontinuous basal facies, shear features, high matrix contents, and crackle and jigsaw breccia textures indicate that the Blue Diamond landslide breccia was emplaced as a rock avalanche. The presence of clastic dikes and flame structures suggest runout occurred over a saturated substrate. Flow transformation into a debris avalanche is ruled out because clast count data show that debris entrainment (< 2%) was not sufficient enough to act as the sole mechanism behind the excessive mobility experienced by the Blue Diamond landslide. Instead, we propose that the excessive mobility was driven by flow entrainment of large Aztec Sandstone boulders and interaction with a saturated runout path substrate that caused a reduced basal frictional resistance, enabling emplacement onto Blue Diamond Hill. We therefore suggest that the landslide breccia was derived from a source area 8.5 km northwest of the Blue Diamond townsite and flowed into the Blue Diamond Hill site where it was deposited onto Moenkopi Formation atop the hill during the Miocene. Due to the new overburden, incompetent gypsum horizons failed within the upper Kaibab Formation stratigraphically below the Moenkopi Formation. These failed gypsum horizons then served as a rupture surface suitable enough to initiate a compound landslide consisting of the overlying Moenkopi Formation and landslide breccia. Emplacement was driven by the head of the Blue Diamond slide block as it slid into its current position in the Blue Diamond area. This secondary emplacement likely ceased by late Miocene to Pliocene time.