Natural scoria cone half-section, East Grants Ridge: A test of basalt pyroclastic eruption models
L. S. Crumpler

Abstract:

The half-sectioned scoria cone exposed on the East Grants Ridge is an exceptional exposure because it preserves the details of the relationship between the near-surface and interior structure of a scoria cone and its surrounding field of basalt. A geo metric reconstruction based on observations of the surface geology and exposures within the natural cross-section, together with as sumptions based on current knowledge of dynamics of scoria cone formation show that the East Grants Ridge scoria cone was a moderately large, fully-developed scoria cone that developed a deep basaltic lava pond now preserved as a columnar-jointed mass of basalt near the center of the section. The lava pond occupying the center of the section in turn fed a fl ow, which breached the north rim of the cone and fl owed northward and mostly westward and now caps the West Grants Ridge. The concept of a lava pond is a departure from many previous interpretations that consider massive “plugs” to be near-surface reservoirs or widened dikes, or dike sheets. More im portantly, many of the observed characteristics within the section agree with predictions of current scoria cone em placement theory that have other wise been diffi cult to test in the absence of a perfectly half-sectioned cone.


Citation:

  1. Crumpler, L. S., 2003, Natural scoria cone half-section, East Grants Ridge: A test of basalt pyroclastic eruption models, in: Geology of the Zuni Plateau, Lucas, Spencer G.; Semken, Steven C.; Berglof, William R.; Ulmer-Scholle, Dana S., New Mexico Geological Society, Guidebook, 54th Field Conference, pp. 155-164.

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