Colombia disaster left little hope of escape
More than 200 dead, scores still missing in debris ‘avalanche’
A lethal mix of gravity, water and dirt combined to create an “avalanche” that tore through a small Colombian city, killing more than 200.
What happened in Mocoa is known as a “debris flow,” which came during an unusually wet season, topped off by a shorter period of intense rain, federal landslide scientist Jonathan Godt says. He says 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,” says 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 boul-
ders and pieces of buildings. For someone experiencing it, an avalanche would be a very accurate description.”
Residents and rescuers clawed through the sea of mud and debris Sunday in a desperate search for survivors, one day after surging rivers overwhelmed the city. Witnesses reporting hearing buildings shuddering and vibrating as the flow crashed through Mocoa. Scores remain missing since the deluge struck after midnight 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 and rocks.
The avalanche is the fourthworst weather-related disaster to strike Columbia, says Jeff Masters, director of meteorology for Weather Underground. He says 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, says debris flows like this one can be more devastating than a flood because the water gives the flow speed and the debris gives it extra punch.
“Because it has all of this water behind it, it’s a really dense, heavy flood,” he says. “Because it’s so dense, it has a lot more momentum and destructive power than water alone.”
Godt says flows like this happen anywhere there are moun- tainous regions. He says the damage varies depending on how steep the surrounding hillsides are and whether trees or other vegetation help “anchor” the wet soil in place. Hillsides burned clean by forest fires or clear-cut via logging tend to be at a higher risk for slides, he says, because there’s less to retain the soil.
Masters says the fact that the disaster struck at night further compounded the danger.
“The debris impacts the houses, knocks them down, so you have a much lower chance of surviving.”
“That very heavy rainfall makes the soil like goo, makes it easy to flow. It just starts sliding down the hillside.” Jonathan Godt, landslide expert