Let me pick August of 2012, as this seems to be my temporal focal point for unnatural mega disasters. Suppose the combination of a slow moving Category 5 hurricane stalls just south of the Big Island, bringing torrential rains to the east side, say, 48 inches over two days.
An earthquake of magnitude 9.0 triggers the eruption of Mauna Loa and Kilauea. This is a stretch, because the largest previously, the Great Kau Earthquake, only was an 8.0. But, say it happens, and, lava begins seeping into those crevices and faults along the line of the previously defined landslide boundaries, weakened by the horrific quake. The extra percolating rain fluid, which also percolates to depth, becomes steam, and, with more heat, continues to expand like superheated gas. The eruptions continue for several days, heating the interstitial fluids, increasing the edifice pore pressure and, through thermal alteration, expanding fault cracks, weakening critical material interfaces and lubricating slip planes. Decoupling along low friction and strength layers occurs at those flow boundaries of Mauna Kea, Mauna Loa and Kilauea. Of course, those 48 inches of rain added an enormous extra weight to the already metastable underground condition.
At 10:04AM on September 6 (I become 72 that day...but I'll be on Oahu, for sure...if not away from Hawaii on a trip), 2012, the collective strains induced by all the above cause a catastrophic failure of the vertical and horizontal extension of dyke intrusions, and the whole monolithic block falls at 250 Km/hour (155 miles/hour) piling up 100 kilometers (62 miles) from the coastline at a depth of 3048 meters (10,000 feet), creating a 100 meter (328 feet—about as tall as the highest building in Honolulu, but only half as high as the Seattle Space Needle) tsunami headed toward Seattle. Stay tuned for what happened.