Is there a word to describe sudden massive alterations to the terrain?

Terraform comes to mind at first, but technically it is not correct. Terraforming is when you alter another planet's terrain or atmosphere to make it more hospitable to terran lifeforms.

I wonder if there a succinct way in a word or two to describe what happens to land when something catastrophic happens, like an impact crater or a flood. What if we directed something like this to happen intentionally in order to recreate a new landscape?

I recently bolded the last sentence because people seem to gloss over and ignore it. So to clarify, I am trying to find a word that describes when we do this artificially and suddenly.

Solution 1:

The best is probably 'cataclysm':

2. A violent and sudden change in the earth's crust.

[cataclysm. (n.d.) American Heritage® Dictionary of the English Language, Fifth Edition. (2011). Retrieved January 16 2016 from http://www.thefreedictionary.com/cataclysm .]

'Cataclysm' has other uses, but any halfway decent context will point up your desired sense.

Second best is what you already used, 'catastrophe', which has a sense much like that of 'cataclysm':

4. A sudden violent change in the earth's surface; a cataclysm.

[catastrophe. (n.d.) American Heritage® Dictionary of the English Language, Fifth Edition. (2011). Retrieved January 16 2016 from http://www.thefreedictionary.com/catastrophe .]

This sense of 'catastrophe' is more remote than 'cataclysm', in that 'catastrophe' is frequently used and misused in the service of other meanings.

If the 'cataclysm' is caused by humans, it will be

anthropogenic adj.
....
2. Caused by humans: anthropogenic degradation of the environment.

[anthropogenic. (n.d.) American Heritage® Dictionary of the English Language, Fifth Edition. (2011). Retrieved January 16 2016 from http://www.thefreedictionary.com/anthropogenic . Note that "anthropogenic degradation etc." is an example provided by the dictionary, not part of the definition.]

If you're looking for an adjective, 'cataclysmic' or 'catastrophic' will fill the bill.

Examples:

A cataclysm caused by a major meteorite impact preceded a major extinction event 65 million years ago. Another such catastrophe surely lies in the Earth's future. The next such catastrophe may be an anthropogenic cataclysm resulting from widespread nuclear war.

Solution 2:

The OP asks:

What if we directed something like this to happen intentionally in order to recreate a new landscape?

The Answer: We nearly did. The tools we planned to use were called Peaceful Nuclear Explosives We would have PNEd the land.

Project Plowshare was the overall United States term for the development of techniques to use nuclear explosives for peaceful construction purposes. It was the US portion of what are called Peaceful Nuclear Explosions (PNE). Edward Teller was one of its champions during the'60s and '70s.

The object was to present a friendly nuclear explosive to the public which would make the public more receptive to nuclear weapons. Proposed uses for nuclear explosives under Project Plowshare 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 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.

The Russians also were part of the PNE program

Peaceful nuclear explosions (PNEs) are nuclear explosions conducted for non-military purposes, such as activities related to economic development including the creation of canals. During the 1960s and 1970s, both the United States and the Soviet Union conducted a number of PNEs. Six of the explosions by the Soviet Union are considered to have been of an applied nature, not just tests

The Comprehensive Nuclear-Test-Ban Treaty of 1996 prohibits all nuclear explosions, regardless of whether they are for peaceful purposes or not.