Winds from protogalactic starbursts and quasars can drive shocks that heat, ionize, and enrich the intergalactic medium. The Sedov-Taylor solution for point-like explosions adequately describes these blastwaves early in their development, but as the time since the explosion ($t - t_1$) approaches the age of the universe ($t$), cosmological effects begin to alter the blastwave's structure and growth rate. This paper presents an analytical solution for adiabatic blastwaves in an expanding universe, valid when the IGM is homogeneous and contains only a small fraction of the total mass density ($��_{\rm IGM} << ��_0$). Using this analytical solution, we examine the role protogalactic explosions might play in determining the state of intergalactic gas at $z \sim 2 - 4$.

37 pages, 11 Postscript figures, LaTeX aaspp.sty file; to appear in Astrophysical Journal, in press (1996 July 10)