Working and sleeping in the crater of one of New Zealand's most active volcanoes was always going to be dangerous.

In September 1914, all 11 men on White Island in the Bay of Plenty were killed by a massive landslide and lahar - a powerful torrent of mud and rock - triggered by the collapse of part of the 300m southwest wall of the crater. But no one knew about the disaster for more than a week.

Whakaari/White Island is a large, mainly undersea volcano whose summit rises 321m above the ocean. It is about 48km from the Whakatane coast.

Volcanologist Dr Tony Hurst says White Island and Mt Ruapehu are currently New Zealand's two most active volcanoes. White Island has a "respectable-sized" eruption roughly every 2-10 years.

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Several attempts at mining sulphur from the crater were made from the 1800s to the 1930s.

Herald report of the White Island disaster in 1914. Source: National Library of New Zealand
Herald report of the White Island disaster in 1914. Source: National Library of New Zealand

The day of the 1914 disaster was probably September 10, but this isn't certain because no witnesses survived. The only survivor was a cat, later renamed Peter the Great. There was also initial uncertainty about the death toll, thought to be either 10 or 11.

The first newspaper reports didn't appear until 11 days later, telling of "the greatest eruption since Tarawera in 1886", and guessing at a date of September 10 or 11, based on the timing of clouds of black smoke, "loud detonations" and an earth tremor that was seen, heard and felt from the mainland.

The volcanic activity or the tremor were thought to have toppled a 300m wall of the crater into the sulphur lake, blocking the main vent and leading to an eruption elsewhere.

But the eruption theory lost favour and it is now thought the collapse of the south-western crater rim caused a lahar to rush through the crater floor, smashing the workers' huts, the manager's house and other mine buildings and shunting them into the sea.

Herald picture of the mounds of debris after the fatal lahar on White Island in 1914. Source: National Library of New Zealand
Herald picture of the mounds of debris after the fatal lahar on White Island in 1914. Source: National Library of New Zealand

Albert Mokomoko, an Opotiki boat owner who ferried supplies to the miners, was the first outsider to witness the destruction. He sailed to the island on September 15, but he didn't have a landing dinghy and couldn't attract attention; nothing seemed amiss and he assumed the men were on another part of the island.

On September 19 - nine days after the likely day of the disaster - he returned and landed. He was confronted by "a scene of desolation", according to the Bay of Plenty Times.

"The effect of the eruption seems to have been to throw the whole hillside overlooking the large lake and camp into the lake and over the whole surrounding area, completely burying the works, dwellings, boats, small wharf and all the inhabitants."

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"The camp was obliterated, the buildings being buried in about 20 feet of sulphurous mud."

A search party dug a trench into the 6m hill of debris where the men's huts had stood, but found no trace of them. There was no possible hope of anyone having survived, the Herald wrote.

More than a fortnight after the disaster, wreckage from the island began washing up on Bay of Plenty beaches, including tram sleepers, pieces of barrels, fragments of boats, but nothing from within the huts.

"The absence of pieces of house furniture suggests that possibly the living quarters were buried where they stood, and the men with them," the Herald said.

No compensation

In a time six decades before New Zealand's a comprehensive accident compensation scheme was established, Florence Maud Williams, of Ponsonby, the widow of one of the victims, labourer Harry Edward Williams, had her claim against his employer's insurer thrown out.

She was faced with proving his death was due to an accident that happened while he was working. But the Arbitration Court ruled too little was known about the disaster to draw the legal inferences needed to establish her case and therefore "she cannot succeed".

The court said it was agreed there was a violent disturbance, the result of natural causes, but whether this was from a landslide, thermal outburst or other cause was impossible to determine.

Although Williams was probably killed on the island or in the sea, the court ruled, it couldn't be determined if this happened while he was at work, going to or from work or outside working hours.

The dead:

• A J C McKim, manager, of Perth, Scotland
• R Lamb
• R Walker
• Harry Edward Williams, of Ponsonby, Auckland
• Stephen H Young, of Opotiki
• A Anderson
• J Byrne
• R Waring
• W J Donovan
• L Kelly
• Robert H Chappell

White Island Tours, which takes tourists to the volcano by boat, tried to find descendants for a remembrance service, says the company's general manager, Patrick O'Sullivan.

"We put feelers out in 2014, coming up to the centenary, to see if we could locate anyone because we were willing to take them out there for a memorial service. No one made contact and we didn't find anyone.

"Only three of the men had children. Most of them were single."

Two other men died on the island around the time of the disaster: John Williams, earlier in 1914, after he was badly burned in an accident with machinery, and Donald Pye who, according to a 1913 newspaper report, was thought to have fallen into the sea.

But the tour company tells a different tale of Pye's demise, one cloaked with mystery since only his boots were found - near the crater.

"He either jumped into the crater or he may have been exploring and fell in," says O'Sullivan.