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 EXPLOSION CRATERS

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��west of El Paso, described by Lee,® are closely similar to the craters in Mexico described above. They are in a level plain of thick stratified river deposits capped by a thin sheet of late basalt. One is a mile in diameter and about 160 feet deep; the other, two miles north, is two miles long and about 250 feet deep. Both are circled by rims of ejecta rising 10 to 200 feet above the plain. The inner slopes are steep and the outer slopes gentle. The ejecta, which lies on a fifteen-foot sheet of basalt, consists of sand, cinders, pumice, and blocks of basalt, and in part, especially near the base, shows irregular bedding with low outward slope. All came from below and was thrown out by an ex- plosion, but the volume is much less than that of the craters. The configuration and structure of the larger crater is shown in Fig. 9. A view is given in Fig. 10.

Lee suggests that the explosion was caused by formation of steam generated by lava forced into the water-saturated sands.

The crater holding Zuni Salt Lake is in the central-western part of New Mexico, about 75 miles south of Gallup. When I published a description of this feature in 1905,^*^ I was inclined to believe that it was due partly to volcanic action and partly to subsidence caused by removal of underlying salt beds by solution. After comparing it with the conditions in other regions, I feel convinced it is an explosion crater. Some of the features are shown in Figs. 11 and 12. It is

����Fig. 11. CoNTOUB Map and Cboss Section op Zuni Salt Lakb in West Cxntbal New Msxico. e^ ejecta ; 8, cretaceous sandstone ; Cj cinder cone ; m, mud and

salt recently deposited by the lake.

• "Afton Craters of Southwestern New Mexico,'' by W. T. Lee, BuU, Qeol, 8oc. Am., Vol. 18, pp. 211-220, pis. 3-4, 1907.

10 "The Zuni Salt Lake," by N. H. Darton, Jour. Geol, Vol. 13, pp. 185- 193, 1905.

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