The treacherous route to the top of Mount Everest

A high-altitude rescue operation is underway on the slopes of Mount Everest after an avalanche killed at least 17 people, including three Americans. Now about 100 people, many of them injured, are trapped on the mountain.

Saturday's earthquake in Nepal triggered an avalanche that buried a mountain base camp packed with hikers preparing for the spring climbing season, reports Vladimir Duthiers of CBS News' digital network, CBSN.

It took the hikers by surprise. Some dove for cover from falling snow, ice and rocks.

Three Americans were among the dead including Google executive Dan Fredinburg, New Jersey medic Marisa Eve Girawong and filmmaker Tom Taplin.

Eight Colorado climbers were stranded, including Ryan Waters of Boulder.

The professional mountain guide called his climbing partner Erik Larsen back home to tell him he was okay.

"He was very lucky and their team was very lucky in the sense that where their base camp, their tents were positioned, was outside of the range of major debris and avalanche zone. And so his first priority was making sure that his team was safe," Larsen said.

Spring is Everest's peak climbing season. Adventurers gather at base camp and wait for local sherpa guides to determine when the weather is just right to scale the summit.

From base camp they ascend to four intermediate camps where they wait and adjust to higher altitudes.

Along the route they pass the frozen bodies of some 200 dead climbers -- a stark reminder of the hazardous conditions.

Just last year, 16 sherpas died in an avalanche that ended the climbing season. It happened at the Khumbu Icefall.

"To get up to camp 1 on Mount Everest, you have to climb what's called the Khumbu Icefall. That is the area of a glacier that is literally pouring over the side of Mount Everest. It's traditionally a very unstable area," Larsen said.

"Because that avalanche and earthquake destroyed so much of that already-fragile Khumbu Icefall, those climbers were trapped there. So all those climbers are now repositioning at camp 1 where they will hopefully be helicoptered off, because the icefall is just completely unsafe," Larsen said.

The dangerous combination of bad weather and the threat of powerful aftershocks have been hindering the helicopter rescues, but conditions seemd to be improving Monday.

Overnight, Jim Davidson, one of the climbers, tweeted: "Weather good on Everest. Evacuation of C1 & C2 going well."