Heart Mountain and South Fork fault systems: Architecture and evolution of the collapse of an Eocene volcanic system, northwest Wyoming: COMMENT

Abstract

We would like to begin by paying tribute to Ed Beutner who passed away in 2008. Ed made significant contributions to the continuing debate over one of the most enigmatic features on the surface of the Earth, the Heart Mountain slide block. Ed will be greatly missed and we wish that he were here to respond to our discussion of his most recent paper—we are certain his comments would have been insightful and of interest to all working on the Heart Mountain problem. In lieu of having Ed's response, we are confident that Tom Hauge will provide a vigorous defense picking up the mantle so aptly held by Ed. We have a number of concerns about the slow/fast model presented by Beutner and Hauge (2009). In our view, many of their arguments supporting slow or incremental movement of the Heart Mountain slide block are not supported by the evidence. In addition, we wish to correct certain erroneous statements and omissions about previous work. In reference to the “phreatomagmatic-hydraulic” model of Straw and Schmidt (1981a, b), Beutner and Hauge (2009, p. 159) state that “… Aharonov and Anders (2006) provided a refined version of the last model.” The Aharonov and Anders model is not a “refined version” of the Straw and Schmidt model as presented in their 1981a and 1981b abstracts. Straw and Schmidt (1981a) wrote: “eruptive centers exerted explosive pressure on water in the regional fracture system” and that the groundwater “exceeded normal lithostatic stress and ‘lift’ the upper plate.” Aharonov and Anders (2006) proposed that the intrusion of dikes heated trapped ground water and reduced pore space via the Skempton effect (Skempton, 1954), thus causing elevated basal pore pressure, enabling sliding of the upper plate along the extremely low 2° gradient. These two models are only …