Man-Made Environmental Disasters

After reading about 10 worst Man-Made Environmental Disasters at the following url: http://www.disasterium.com/10-worst-man-made-disasters-of-all-time/ and/or searching the web and history, and/or using your own knowledge/interests and experiences, please list top three disasters for you. Explain why you choose those three, what are you most shocked with, what are you most devastated with, what are you most interested in attacking to solve as a future civil and environmental engineer.