TAAL VOLCANO, Philippines — The gray ash is knee-deep. It covers homes, trees and the bloated cadavers of cows and horses, their limbs protruding at unnatural angles in the shadow of a brooding volcano that could re-explode at any moment.
“My home is now gone,” said Melvin Mendoza, 39, a boatman who returned on Tuesday to Taal, the volcanic island in the middle of a freshwater lake just 40 miles south of Manila, which erupted on Sunday like an atomic bomb mushroom cloud.
The toxic ash and smoke, reeking of sulfur and other noxious gases, have transformed the verdant island, a popular tourist spot, into a vast carpet of lifeless gray.
At least 30,000 people in a nine-mile radius of surrounding towns have fled, and the United Nations says as many as a half-million residents remain at risk. For now, Taal is not habitable, and volcanologists say a new and perhaps more powerful eruption is possible.
Despite government warnings, Mr. Mendoza and a few other residents of the island ventured back from emergency shelters on Tuesday to see firsthand what remained of their homes, and perhaps salvage a few belongings. A reporter and photographer from The New York Times accompanied them.
Among the first challenges they faced as they sloshed ashore from a motorized canoe was the two feet of ash. It was difficult to see precisely where the water ended and the land began. Hundreds of dead, ash-coated tilapia bobbed in the gentle current, injecting the smell of rotting fish into the sulfur-scented air.
In some places, rain had already hardened the ash, like crusty snow, making it relatively easy to walk over. Elsewhere, the ash was still soft and treacherous.
Mr. Mendoza choked back tears as he salvaged a plank of wood from what had been his house.
“We had happy memories here,” he said. “The island sustained our livelihoods, but also took everything back. Everything’s gone in the blink of an eye.”
Coconut trees are now blackened stumps, and the menacing mountain was still belching plumes of smoke and ash with ultrafine particles that are dangerous to breathe.
Just steps away from a horse’s cadaver stood the remains of Taal’s tourist office, a two-story cement building that was once the busiest on the island, hosting more than 2,000 volcano visitors a year. All the other buildings nearby have collapsed.
One of the Philippines’ most active volcanoes, Taal roared to life with a jolt on Sunday, catapulting ash a mile high and triggering dozens of earthquakes that panicked residents as far away as the Manila metropolitan area, home to nearly 13 million people.
The government’s Philippine Institute of Volcanology and Seismology said Tuesday that Taal was at the fourth of a five-step alert level, meaning that another hazardous eruption was possible within hours to days. Warning of a heavy and prolonged ash fall, it said all residents should stay away.
A thick column of ash was rising from the Taal crater, visible for miles around and posing a threats to aircraft.
The danger is not limited to ash, smoke and lava flows. The volcano institute also warned of a possible tsunami from the earthquakes that might accompany another eruption. They could send walls of suddenly displaced lake water surging toward the shore, crushing and inundating everything in the way.
The Taal volcano has erupted about 35 times in the last few hundred years, volcanologists say. The last time was in 1977.
There was little warning before Taal erupted again on Sunday, and residents of the island and nearby towns in Batangas Province scrambled for safety, forced to leave everything behind.
Mr. Mendoza said he felt lucky. His wife, Jasmine, 34, and two young children, ages 14 and 10, escaped unscathed.
“As long as we’re alive, there’s hope,” he said.
Others who returned in small canoes on Tuesday found that some of their livestock had survived. One farmer was miraculously able to load a water buffalo aboard a canoe. Another rummaged through a crack in the ash-covered earth and emerged with a plastic bag of stuffed toys.
“These are owned by my nieces,” he said as he pointed to a mound. “Our house is under that.”
Amid reports that the government may permanently bar residents from going back to the island, the men risked arrest by the Coast Guard, which has deployed officers in towns surrounding the volcano to ensure a complete evacuation.
For Roger Holgado, a 56-year-old resident of the island, not going home was not an option. He was born on the island and has spent his whole life there, he said.
Mr. Holgado witnessed the last eruption four decades ago, when he was just a teenager.
“I have seen the island being restless before, but it has always calmed down,” he said. “I’m sure it will again this time. Because I don’t know what we will do.”
Mr. Holgado said his family had operated a small lottery business on the island, and it provided for him, his wife and nine children.
Volcanic eruptions are not an anomaly in the Philippines.
Last January, an eruption at the most active volcano in the island nation — the Mayon, in Albay Province, about 200 miles east of the Taal — prompted a Level 4 alert as it generated up to 1,600 feet of lava fountains and ash fell on two nearby villages.
Renato Solidum, the government’s chief volcanologist, said Tuesday that Taal had been emitting lava ever since its eruption, accompanied by significant earthquakes — all pointing to more trouble.
“The condition of Taal Volcano is dangerous, and an explosive eruption is possible within hours,” he said.