2012 Cascadia earthquake

The 2012 Cascadia earthquake was a 10.2 magnitude earthquake that occurred on September 1, 2012 at 9:00 AM PDT. It was the fourth largest earthquake in recorded history, and the first recorded to reach and exceed 10 on the Richter scale. The main cause of the quake was a major shifting of the Juan de Fuca Plate beneath the North American Plate to the east by nearly a hundred miles. The exposure of the magma beneath the plate unleashed the 1100 foot-high megatsunami by expansion of the water through superheating.

History
The earthquake itself was felt in Seattle, Tacoma, Portland, Salem, Eugene, even as far south as San Jose, and as far east as Boise. The tsunami generated reached over 1000 feet high. The last places to be hard hit were Eureka, Fortuna, and Ferndale, California, where the wave was still 105 feet high when it reached as far south as Bodega Bay, and nearly 67 feet at Inverness. Tidal gauges at Fort Point and Helmet Rocks near the entrance to San Francisco Bay recorded a 50 foot wave that was only partially dissipated before entering the bay, where it crashed into the support towers of the Golden Gate Bridge and caused severe erosion at Alcatraz. And, in San Francisco, all of what remained of the old eastern span of the Bay Bridge collapsed into the bay, though all of the new eastern span remained intact (it would later be completed in the spring of 2013).

Seattle
The megatsunami swept through Olympia about fifteen minutes before it struck the Seattle-Tacoma area, after Seattle was struck by its own earthquake, a magnitude 9.5. The wave converged on Seattle from Puget Sound and from the Olympia area around 1:00 PM. Though the tallest buildings in Seattle were taller than the 700 foot-high wave, they were still twisted and gutted by the force of it, while the other skyscrapers of downtown Seattle simply exploded from the pressures exerted on them after the city's earthquake. The Space Needle, already tilted by the earthquake, and in danger of falling, was ripped from its weakened foundations and carried by the Puget Sound wave into the Olympia wave, where it was dropped onto the then gutted underwater ruins of downtown Seattle.

Portland and Western Oregon
The wave was channeled up the Columbia River and flooded Portland with multiple 100+ foot-high waves, destroying yet another major city. The Williamette River Valley was flooded by the waves as far south as Eugene, reforming the post-glacial Lake Allison, with the exception that the land between Portland and the ocean became an island when the new 'lake' breached at the Eugene end, rushing out through another fissure created by a 10.0 aftershock, linking with Pacific and creating a permanent inlet. Salem was heavily damaged as well, when a still 59 foot-high wave crashed through downtown and destroyed the state capitol building, leaving two US states without working governments.

Aftermath
The Pacific Northwest was nearly erased from existance, and the damage to the region was beyond irreparable. Over 7.7 million died (mainly in North America) as a result of the tsunami's Pacific-wide impact, which was felt as far away as Papua New Guinea. The earthquakes, (M10.2, M9.5) and the aftershock (M10.0), triggered the eruptions of every Cascade volcano, with the exception of Mount Mazama (Crater Lake), creating a wasteland out of a once striking region. The ash cloud drifted freely, but mainly to the north-nortwest, raining half a foot of ash on Juneau, Alaska, and a foot in Vancouver. The farthest east it reached was Yellowstone, but the effects from the ashfall itself was minor, with total accumulations reaching a centimeter. The seismic shocks reverberated throughout the planet, triggering moderate-sized quakes as far away as Eastern Europe and stopping the earth's axis rotation for nearly five seconds, causing major flooding around the globe, as bodies of water were slightly jerked out of alignment with their basins, and underground water began to rise through the fracturing crust.