QUOTE (Emma_Acid_88 @ Jun 26 2008, 02:03 AM)

I think since the 50s most of the tests were exploded underground (leaving much less fall out), which results in the craters we see (the blast evaporates* the rock under the surface creating a gap). Atmospheric nuclear explosions don't cause craters.
Actually, if you read the second link I posted, about 2/3 down the page they talk about "Cratering Tests":
QUOTE
The last completely above ground test at NTS took place on 17 July 1962. There were, however, several cratering tests conducted in support of Project Plowshare. This endeavor called for the use of nuclear explosives for excavation of canals, harbors, and mountain passes. To prove the feasibility of such peaceful uses of nuclear explosives, devices were buried at a depth that would allow the maximum amount of soil to be displaced.
Other links:
http://en.wikipedia.org/wiki/Operation_PlowshareQUOTE
Operation Plowshare, better known as Project Plowshare, not to be confused with the anti-nuclear Plowshares Movement, was the overall United States term for the development of techniques to use nuclear explosives for peaceful construction purposes. The phrase was coined in 1961, taken from Micah 4:3 ("And he shall judge among the nations, and shall rebuke many people: and they shall beat their swords into plowshares, and their spears into pruning hooks: nation shall not lift up sword against nation, neither shall they learn war any more"). It was the U.S. portion of what are called Peaceful Nuclear Explosions (PNE). The Soviet Union had a similar program of testing as well for many years. The Soviet program was titled Nuclear Explosions for the National Economy.
Suggested usage
Proposed uses included widening the Panama Canal, constructing a new sea-level waterway through Nicaragua nicknamed the Pan-Atomic Canal, cutting paths through mountainous areas for highways, and for connecting inland river systems. Other proposals involved blasting underground caverns for water, natural gas, and petroleum storage. Serious consideration was also given to using these explosives for various mining operations. One proposal suggested using nuclear blasts to connect underground aquifers in Arizona. Another plan involved surface blasting on the western slope of California's Sacramento Valley for a water transport project. At the end of the program, a major objective was to develop nuclear explosives, and blast techniques, for stimulating the flow of natural gas in "tight" underground reservoir formations.
Nuclear explosives have never been used for commercial engineering purposes in the United States, but the concept has been tested.
http://en.wikipedia.org/wiki/Sedan (nuclear test)QUOTE
Storax Sedan was a shallow underground nuclear test conducted at the Nevada Test Site at [show location on an interactive map] 37.177048° N 116.046653° W by the United States on July 6, 1962 as part of Operation Plowshare program to investigate the use of nuclear weapons for mining, cratering, and other civilian purposes.
The blast had a yield of 104 kilotons (435 terajoules) and displaced more than 11 million tonnes (12 million short tons) of soil and resulted in a radioactive cloud that rose to an altitude of 3.7 km (12,000 feet). The radioactive dust plume headed northeast and then east towards the Mississippi River. It created a crater 100 m (320 feet) deep and has a diameter of about 390 m (1,280 feet). It is about 21 km (13 miles) away from Groom Lake.
Cz