KATHMANDU, Nepal — A week after powerful flash floods devastated riverside communities in Tibet and Nepal and killed more than 1,000 people, rescuers are still racing to locate survivors who may be trapped inside around a dozen hydro-power plants buried under the mud.

But to rescue them, one man overseeing part of a rescue says, first, they have to find the tunnels where the men and women are believed to have fled. Just finding the tunnels is an achievement, amid a post-flood landscape that tunneling expert Arnold Dix described as “like a bomb’s gone off.”

The effort to locate the trapped workers was just one part of a sprawling, complex rescue and humanitarian operation that some 21,000 Nepali security forces and rescuers have been undertaking since floods left some 4,000 people missing, according to a Wednesday briefing by the spokesperson for the Ministry of Foreign Affairs, Lok Bahadur Poudel Chhetri.

Nepal’s army is leading rescue efforts for the trapped hydropower workers, and on X, the military shared a video of khaki-clad men pulling themselves on ropes in what appeared to be a muddy, dripping, narrow tunnel. The flood was triggered after part of a glacier about 3,000 feet wide snapped off a mountain and tumbled some 4,000 feet into a river valley. The water barreled the debris, mud and ice forward, smashing away buildings, wiping away riverbank communities and burying hydropower stations that once dotted the landscape, particularly along the Trishuli River.

“It’s removed the power stations from the surface, like they’re just not there,” Dix told NPR. “So the first problem we had is just finding them. So you’re presented with a moonscape.”

Dix said the ground has risen between 30 and 50 feet in some areas, causing the river to shift, and the force of the water had caused about a dozen power stations to be completely or partially destroyed. “And so in each of them, because there’s tunnels and powerhouses, we’ve potentially got people trapped,” Dix said.

Dix says rescuers are relying on advanced mapping techniques to locate the tunnels that lead into the turbine houses. “And the Goldilocks zone where we think people may have survived is actually in the turbine houses,” Dix said.

Dix was assigned to oversee the tunneling rescue of people in one hydropower plant called Trishuli 3A, where dozens of people are feared trapped.

He said in the past few days, rescuers dug down into the entrance of the tunnel, which was once open to the air. “It’s now underneath the river,” Dix said. And “we found there were huge boulders,” he said, “thrown right into our tunnel and mud.”