Colombians return to dig through debris-filled city
Deadly slides kill more than 200, many still missing
Residents and rescuers resumed the desperate search for survivors Sunday in the Colombian city of Mocoa, one day after surging rivers drove a wall of water and debris through the city, killing at least 207 people and injuring 200 more.
Scores of people remained missing amid the vast sea of mud, debris and destruction, Colombian President Juan Manuel Santos said. He said he would help lead the effort to restore water service and power to the devastated area.
The tragedy was triggered by a deluge that dumped 5 inches of rain on the region Friday night, about half the amount of rain the region normally gets for the entire month of March, Santos said. Early Saturday, the Mocoa River and its tributaries overwhelmed their banks.
But a lethal mix of gravity, water and dirt combined to create the “avalanche” that tore through the city.
What happened in Mocoa is known as a “debris flow,” which came during an unusually wet season, topped off with a shorter period of intense rain, federal landslide scientist Jonathan Godt said. He said he reviewed images and video of the Mocoa disaster, noting the mountains surrounding the city.
“That very heavy rainfall makes the soil like goo, makes it easy to flow. It just starts sliding down the hillside,” said Godt, coordinator of the U.S. Geological Survey’s landslide hazards program.
“My guess is that it was moving very fast and would have been full of rock and boulders and pieces of buildings. For someone experiencing it, an avalanche would be a very accurate description.”
Witnesses reported hearing buildings shuddering and vibrating as the flow crashed through Mocoa. Scores remain missing since the deluge struck early Saturday when many people were sleeping, washing away trees, vehicles, houses and everything in its path.
Pictures posted to social media show bridges wiped away, piles of debris in the town center, and overturned vehicles tumbled amid tree limbs, rocks and fencing.
The avalanche is the fourthworst weather-related disaster ever to strike Columbia, said Jeff Masters, director of meteorology for Weather Underground. He said the damage is great because the city was built in a potentially dangerous location: at the bottom of mountains, alongside a riverbed.
Godt, who has created smallscale landslides in Oregon for research, said debris flows like this one can be more devastating than floods because the water gives the flow speed, and the debris gives it extra punch. He said the flow would have been loud: Think water rushing, boulders crashing and trees being torn apart.
“Because it has all of this water behind it, it’s a really dense, heavy flood,” he said. “That mixture can move at 3540 mph, and because it’s so dense, it has a lot more momentum and destructive power than water alone.”
Godt said flows like this happen anywhere there are mountainous regions. He said the damage varies depending on how steep the surrounding hillsides are and whether trees or other vegetation help “anchor” the wet soil in place.
“Gravity is always working to drag the mountains down, and water changes the strength of the material,” he said. “A layperson’s description of this as an avalanche of mud and rock would be absolutely accurate.”
Masters said the fact that the disaster struck at night further compounded the danger: People waking up to such a calamity might have had no way to escape the flows.
“The debris impacts the houses, knocks them down, so you have a much lower chance of surviving,” he said.