Natural disasters doomed early civilization

http://news.yahoo.com/s/ap/20090119/ap_on_sc/sci_ancient_calamity/print

They found that a massive earthquake, or series of quakes, struck the seismically active region, collapsing walls and floors and launching landslides from barren mountain ranges surrounding the valley.
In addition, layers of silt indicate massive flooding followed.
Then came El Nino, a periodic change in the winds and currents in the Pacific Ocean, which brought heavy rains that damaged irrigation systems and washed debris into the streams and down to the ocean, where the sand and silt settled into a large ridge, sealing off the previously rich coastal bays.