From the large amount of data available for explosion craters in the desert alluvium at the Nevada test site it has been possible to establish very reliable relationships among charge size, depth of burst, crater radii, and crater depths. A scaling law for crater dimensions of W1/3.4 is derived, together with an efficiency factor for nuclear explosives relative to high explosives. In addition, a curve for the dependence of crater radii and depth on the depth of burst of the explosive is given.

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.

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P r i n t e d in USA. P r i c e $ 5.50 (includes two v o l u m e s , P a r t s 1 and 11).AvaiJ.able I r u r n the Office o f '~e c h n i c a 1 S e r v i c e s , D e p a r t m e n t of C o m m e r c e Washington 25, D. C. PREFACEThe Geophysical ~a b o r a t o r~/~a . w r e n c e Radiatidn L a b o r a t o r y C r a t e r i n g Symposium developed, . i.n l a r g e p a r t , f r o m a suggestion of D r . Gerald W':: $ Johnson,. Associate Director of the Lawrence Radiation Laboratory. D r .Johnson, a s d i r e c t o r of the Plowshare P r o g r a m f o r industrial application of nuclear explosives, was i n t e r e s t e d in the u s e of l a r g e scale explosibn c r a t e r s \ f o r excavation purposes. This i n t e r e s t l e d to studying m e t e o r c r a t e r s on the e a r t h . and moon, and i t o c c u r r e d . t o -him that a joint symposium .between .the s c i e n t i s t s who w e r e i n t e r e s t e d i n explosion c r a t e r s and those who w e r e in-,.t e r e s t e d in . t e r r e s t r i a l and lunar m e t l o r c r a t e r s might prove v e r y beneficial .to both groups. The p r o p o s a l ' g r e a t l y i n t e r e s t e d Dr. Philip Abelson, ~i r e c t o a of the Geophysical Laboratory, who promptly offered the facilities of the Geophysical ~a b o r a t o r~ and began t h e ' t a s k of organizing the &eefin.g. . .The succ e s s of the sympobium was attributable in no s m a l l m e a s u r e to the participa-.tion of ,Qr. Abelson and the Geophysical Laboratory and we a r e grateful f o r t ' the hospitality which they extended t o the participants. P a r t i c u l a r thanks m u s t a l s o go t o Dr. Gordon F. MacDonald, National Aeronautics and Space Administration, and Dr t Wilmot N. H e s s , 7 Lawrence Radiation ~a b o r h t o r~, who a r r a n g e d the agenda and compiled the l i s t of s p e a k e r s and invitees.The symposium was held at, the Geophysical L a b o r a t o r y of the Carnegie Institute, Washington, D. C . , on M a r c h [28][29] 1961.. Attendees included m o s t 6f the e x p e r t s in explosion' and i m p a c t c r a t e r s in the United States and ' :. .~a n a d a . Following introductory r e m a r k s by D r . . W. T.I P e c o r a , U. S. Geological Survey, Washington', D. C . , . t h e symposium plunged into the subject I . . J. -,-Now on leave of absence to s e r v e a s A s s i s t a n t to the S e c r e t a r y of Defense on Atomic Energy M a t t e r s and a s C h a i r m a n of Military Liaison Committee.Now with National Aeronautics and Space Administration.of c r a t e r i n g . The symposium broke up l a t e in the afternoon of the second day with a feeling s h a r e d by a l l that the two days spent discussing c r a t e r i n g w e r e days well spent.T h e s e proceedings a r e published i n two volumes, designated P a r t s I ; ;and 11. All the p a p e r s delivered a t the meeting a r e included in roughly the o r d e r in which they w e r e presented. P a r t I contains the p a p e r s given on the f i r s t day of the meeting, and P a r t I1 c...

A summary of the cratering and radioactivity release data from project Danny Boy, a recent 0.42‐kt nuclear cratering detonation in basalt, is presented. The detonation was at a depth of 33.5 m and produced a crater about 32.5 m in radius and 19 m deep. Comparison of the crater dimensions with past cratering results in basalt shows that the Danny Boy crater agrees with these data when W1/3.4 scaling is used and an equivalence between chemical and nuclear explosives is assumed. Integration of the fallout pattern shows that about 4 per cent of the radioactivity produced in the explosion escaped from the crater and appeared as fallout. The disposition of the radioactivity in the crater area and in the fallout is given. On the basis of the above results, it is concluded that both the cratering results and the radioactivity‐release results are well within predictions made before the event.