Watch: Ordinary Americans Become Heroes in the Wake of Harvey Devastation

In the wake of Hurricane Harvey’s horrific destruction in Houston, Texans are pulling together to help with rescues, food shelter, and support.

The epic scale of the devastation is now slowly coming into focus.

"This is a storm that the United States has not seen yet," the head of the Federal Emergency Management Agency said.

"FEMA is going to be there for years," administrator Brock Long said Sunday on CNN's "State of the Union."

He added, "This disaster is going to be a landmark event."

 As the president tweeted, experts are now calling Hurricane Harvey a "500-year flood."

Disasters tend to bring out  the worst in some people and the best in others.