Nuclear craters and preliminary theory of the mechanics of explosive crater formation

Abstract

Four nuclear craters have been produced at the Nevada test site. Three were from 1.2‐kiloton nuclear explosions in desert alluvium, a sand‐gravel mix, and the fourth was from a 115‐ton nuclear explosion beneath the sloping side of a bedded tuff mesa. Comparison of these craters with high‐explosive craters in alluvium shows that, within experimental error, the craters produced by subsurface nuclear explosions are quite comparable with those produced by equal yield chemical explosions. Experimental data from these nuclear and chemical explosive cratering programs and theoretical machine calculations of the behavior of underground explosives make it possible to construct a picture of the major mechanisms that contribute to the formation of explosion craters. These mechanisms include compaction and plastic deformation of the medium immediately surrounding the explosion, spalling of the surface above the explosion by the tensile wave generated at the free surface of the ground, and acceleration of the fractured material overlying the explosion cavity by the gases trapped in the cavity, before and during their escape. The role that each mechanism plays changes with the scaled depth of burst of the explosive and to some extent with material. The contribution that each makes is outlined for four typical craters representing surface, shallow, optimum, and deep burial depths. For surface burial, plastic deformation and compaction are the principal actions; for shallow burial depth, spall is the dominant feature; for optimum depth, gas acceleration becomes the most important mechanism; and for deep burial, subsidence into the cavity produced by plastic deformation and compaction is the major factor. The differences to be expected between explosion craters and craters resulting from impact explosions such as those produced by meteors are examined. The relative contribution of each of these mechanisms is also estimated for apparent crater depth vs. depth of burst.

Scaling multiblast craters: General approach and application to volcanic craters

“…Crater radii, for example, change by a factor of less than 3 when varying the substrate material from hard rock to wet sand [e.g., Rooke et al , ; Rickman et al , ; Dillon , ], but the order of crater radius is given by the length‐energy scale. Radius changes due to change of explosive types from ammonium‐based chemical to nuclear explosives seem to be of similar order [ Rooke et al , ; Nordyke , ]. Crater volumes vary as a function of the scaled explosion depth , where d is the unscaled distance from the explosion location to the surface and p = 1/3 for “cube root” scaling or 1/4 for quarter root scaling [ Vortman , ].…”

Observations at terrestrial impact structures: Their utility in constraining crater formation

“…2) arose out of observations at simple terrestrial impact structures. Early interpretations ascribed this breccia in-filling of the true crater to some form of fallback material from the "explosion" resulting from the impact (cf., Nordyke 1961).…”

Magnetic Reconnaissance of Sierra Madera, Texas, and Nearby Igneous Intrusions

“…For example, a t Meteor Crater, Ariz., the Supai sandstone was intersected by several of the Barringer drill holes a t its normal level about 900 feet below the center of the crater (Merrill, 1908). Furthermore, there is no indication of central uplift in any published cross sections of ancient impact craters (Beals et al, 1960), high-explosive craters (Murphey & Vortman, 1961), or nuclear explosion craters (Nordyke, 1961). It is hardly necessary to mention that Sierra Madera is too small for isostatic uplift t o have occurred.…”