Floods result from many different situations.
Flooding can follow volcanic activity and earthquakes. As Earth shifts, tsunamis race across oceans, and water vapor is released into the atmosphere.
Hurricanes whip up merciless waves that cause flooding. Melting glaciers can raise the level of lakes and rivers beyond their boundaries, as can heavy, incessant rain or snow.
Natural disasters, such as landslides, avalanches, natural dike breaks, and soil erosion, can bring on massive flooding. Of course, in civilization’s attempt to make Earth conform to people’s needs, we have created our own flood dangers.
The famous flood in Johnstown, Pennsylvania, in 1889 seems to have been caused by vacation homeowners neglecting to repair the dikes along the lake created for their enjoyment.