Great American Flood.
This is the first in a series of maps based around a natural disaster in the United States that would make 9/11 like a pinprick. In the Western United States, during the summer of 1983, the Glen Canyon Dam was on the verge of failure. The POD for this disaster would be opening the spillway in late June instead of early June, which would allow for the failure of the Dam. According to a 1928 study if Glen Canyon were to fail Hoover Dam would fail and destroy every community downstream (
https://en.wikipedia.org/wiki/Hoover_Dam#Planning_and_agreements). This increased flow would cause the River to change course and flow into the Salton Sink thus flooding the Imperial Valley creating the 8thlargest lake in the United States.
This map shows the Colorado River from Glen Canyon to the US/Mexico Border. The red splotches without borders are the areas of major dam failure as well as areas where the river has diverted. The spots with boundaries are cities that are critically affected. The cities of Laughlin, Lake Havasu, Yuma and the cities of the Imperial Valley would disappear and the death toll would be in the hundreds of thousands as there would have to time to evacuate. Cities such as Las Vegas, Phoenix and Tucson would be practically abandoned overnight. States such as Wyoming, Utah, Colorado, New Mexico, Arizona and Nevada would loose significant power from just the loss of the Glen Canyon Dam. From the loss of the Glen and Hoover Dams the Western United States have been plunged into a ‘dark age’. The agriculture industry of California would be on the verge of collapse and population of Los Angeles would halve but, this is just California. Southern Nevada, Arizona, Southern Utah and Western Colorado would be drastically changed in regards to population as well as political standing.
With the POD in 1983 this would place the disaster in midst of the Reagan Presidency, which would cause the President we know of in OTL as ‘international’ (I only say this because of his view on communism as well as: Lebanon, Grenada and the Contra Conflict) to focus on internal pressures. As a result this disaster would probably flip the United States to isolationism and lead to a very peculiar 1984 election.
All of the political repercussions of this disaster will be featured in updates. Please let me know your opinions.