I have read that launching multiple ICBMs at once makes a really big and loud explosion. Does it also do damage to a large surrounding area as well? Like could you launch a hundred or so ICMBS and blow up an entire continent?

Also, what effect do they have on the terrain? Do they render terrain completely useless until cleaned like in Civ3? Can enough of them wipe out an entire city completely (would be more realistic)?

I have read that launching multiple ICBMs at once makes a really big and loud explosion. Does it also do damage to a large surrounding area as well? Like could you launch a hundred or so ICMBS and blow up an entire continent?

Also, what effect do they have on the terrain? Do they render terrain completely useless until cleaned like in Civ3? Can enough of them wipe out an entire city completely (would be more realistic)?

Short Answer:
A. No, same damage Area
B. Fallout on Terrain
C. Pretty much
D. Down to Size 1