The daunting conditions faced by the recovery team on Friday underscored the sheer power of the initial eruption — which blasted rocks and sulfurous debris into the sky, filled the air with acidic gas and smothered the island with layers of ash — and again raised the question of why tourists had been allowed onto the island despite a recent rise in volcanic activity.

The authorities had held off for days on sending the team to White Island, also known by its Maori name, Whakaari, because experts said it could erupt again at any time. But they moved ahead with the mission on Friday, recognizing the need to bring peace to the victims’ loved ones. Even as the team was trekking through sludge-like ash, the odds of an eruption stood at 50 percent to 60 percent, according to volcanologists.

The troops landed on the island at 8 a.m., said their on-the-ground commander, who was made available to discuss the operation with reporters on the condition that his identity not be disclosed.

A sentry was monitoring the volcano for signs of change in its activity, and teams on boats anchored nearby were in a state of alert, ready for a sudden evacuation. A backup crew of special operations forces, wearing the same protective gear as the team on the ground, was in a rubber dinghy on standby.