An unstable ice block dangerously hanging over the key trail on Mount Everest , high travel costs and increased permit fees haven't deterred hundreds of climbers from attempting to scale the world's highest mountain. Around 410 climbers and an equal number of their Nepali climbing guides are at the base camp gearing up for the ascent to the nearly 8,850-meter-high (around 29,000-foot-high) peak this month during the much anticipated window of good weather on the mountain. Climbers began gathering last month at the base camp, which is at an altitude of 5,300 meters (17,340 feet). But for more than two weeks, a massive and unstable block of ice, or serac, stalled them from moving further up the peak. “Icefall doctors,” the elite guides deployed by the Sagarmatha Pollution Control Committee, or SPCC, to lay the yearly climbing route by setting ropes and securing aluminum ladders over crevasses, usually finish the task by mid-April. But not this year.…