http://SaturnianCosmology.Org/ mirrored file
   For complete access to all the files of this collection
        see http://SaturnianCosmology.org/search.php
  ==========================================================



   PNAS
   Proceedings of the National Academy of Sciences of the United States
   of America

K-Ar ages of Pleistocene lava dams in the Grand Canyon in Arizona

    1. G. Brent Dalrymple*,/- and
    2. W. K. Hamblin/=

    1. 


    ^*College of Oceanic and Atmospheric Sciences, 104 Ocean
    Administration Building, Oregon State University, Corvallis, OR
    97331; and ^/=Department of Geology, Brigham Young University,
    Provo, UT 84602

    1. Contributed by G. Brent Dalrymple

Abstract

   At least 13 times during the Pleistocene Epoch lava flowed into the
   inner gorge of the Grand Canyon and formed lava dams, as high as 600
   m, that temporarily blocked the flow of the Colorado River. K-Ar ages
   on these lava dams indicate that the seven youngest formed within a
   short period of time between about 0.6 and 0.4 mega-annum (Ma). The
   physiography of the lava dam remnants within the canyon shows that
   each dam was destroyed by erosion, the Colorado River rapidly reaching
   its pre-existing grade level, before the next dam was emplaced by new
   eruptions. The total time for emplacement and destruction for an
   individual lava dam was probably as little as 0.01-0.02 million years.
   The K-Ar ages of the two oldest dams, the Lava Butte dam (0.577 ±
   0.054 Ma) and the Prospect dam (0.684 ± 0.051 Ma) are somewhat younger
   than the physiography of their remnants suggest.
     * radiometric dating/volcanism/basalt/potassium-argon