a1k0n

b[2080];main(j){for(;;){printf("\x1b[H");for(j=1;j<2080;j++)b[j]=j<
2000?(b[j+79]+b[j+80]+b[j]+b[j-1]+b[j+81])/5:rand()%4?0:512,j<1840?
putchar((j%80)==79?'\n':" .:*#$H@"[b[j]>>5]):0;usleep(20000);}}

update: fixed a crashing bug. It has other issues with uninitialized data, though.