Calculations for surface dirt volume from a 1 Megaton surface burst

				.  .  .
			   .       |        .
		       .      200' |  h         .
		    .   Dirt       |      Dirt     .
		 ._________________|__________________.
	      .   \     r=500'     |  r=500'             .
	    .       \              |             Air       .
	  .           \  R         |                         .
	.               \          | R-h = 525'                .
      .                   \        |                             .
     .  R=r^2 + (R-h)^2     \      |  v=pi/3*h^2*(3*R-h)          .
    .   R^2=r^2+R^2-2Rh+h^2   \    |        or                     .
   .    2Rh=r^2+h^2             \  |  v=pi/6*h*(3*r^2 + h^2)        .
  .     R=(r^2+h^2)/2h            \|                                 .
	R=(500^2+200^2)/2*200         v=8.273e7'^3
	R=25e4+4e4/4e2
	R=29e4/4e2=7.25e2=725'        V=4/3*pi*R^3 = 1.596e9'^3
				      v/V = 5.18%

  v = volume of a spherical segment   V = volume of total sphere @ radius R