4 August 2010

A tale of death, derring-do and barometers

Posted by vivienne

Around noon on 8th June 1924, mountaineer Noel Odell saw the ‘whole summit ridge and final peak of Everest unveiled’. Through the mist, he glimpsed fellow climbers George Mallory and Andrew Irvine climbing over an obstacle on the Northeast ridge of the mountain. Then clouds engulfed Mount Everest again and the pair vanished from sight. Odell was the last person to see them alive.

No one knows if Mallory and Irvine reached Mount Everest’s summit before they died, 29 years before Edmund Hillary and Tenzing Norgay officially conquered the peak. Their disappearance remains one of mountaineering’s most compelling mysteries that – if solved – could rewrite history. Now scientists think they’ve shed some light on the climbers’ final hours thanks to some hand-drawn maps and the humble barometer.

Unravelling the secret behind Mallory and Irvine’s fate has traditionally required feats of derring-do. Statistically, one in ten attempts on Everest end in death. At the highest altitudes in the notorious “death zone”, the human body begins to shut down. Reaching the top is a race against time. Looking for clues like climbers’ bodies or discarded equipment means risking your life.

Despite the dangers, several expeditions have sought to find out more about the historic 1924 expedition. George Mallory’s body was found in 1999 by a team gathering evidence about the pair’s fate, but the discovery left many questions unanswered. Mallory and Irvine’s cameras weren’t with the body. A photo of Mallory’s wife, which he promised to place on the summit, was also missing – raising the tantalising possibility he reached the top.

A second expedition was launched in 2001 to find Irvine’s body, but was cut short when the team stumbled upon five mountaineers stranded overnight without oxygen near the summit. During one of Everest’s most difficult rescues, they successfully saved four of the stricken climbers. Unperturbed, one of the expedition team and a British climber returned to the mountain in 2007 to retrace Irvine and Mallory’s steps in 2007 with a film crew and some replica equipment.

But is something “curiously absent” from all the “vigorous debate” and discoveries so far? Dr John Semple and Professor Kent Moore from the University of Toronto thought so. “The weather is perhaps the greatest unknown”, Professor Moore said in a press release about the paper he and Semple have published in Weather, the journal of the Royal Meteorological Society.

What makes it “even more remarkable” weather has been overlooked, according to Semple and Moore in their paper, is the historic 1924 Expedition was notable for collecting some of the earliest meteorological data around Mount Everest. Expedition members like Mallory and Irvine measured air (barometric) pressure every day at 8:30am at Everest Base Camp (5029m), and temperature three times a day at Base and several higher camps.

Semple and Moore uncovered the Base Camp data at the London’s Royal Geographical Society library. Although the data were published in a table in a 1926 report on the expedition, they were the first to use it to find clues to Mallory and Irvine’s disappearance. Semple and Moore also used sea-level air pressure maps hand drawn by the Indian Meteorological Society.

“We analysed the barometric pressure measurements and found out that during the Mallory and Irvine summit attempt, there was a drop in barometric pressure at base camp of approximately 18mbar. This is quite a large drop, in comparison the deadly 1996 ‘Into Thin Air’ storm had a pressure drop at the summit of approximately 8 mbar,” said Moore in a press release. “Into Thin Air” tells of a ‘rogue storm’ that led to the deaths of eight climbers and stranded several others.

Falling air pressure heralds a storm because it means air is unstable, rising and exerting less force on the ground. The air cools as it rises, forming clouds and rain. Wind speeds increase as air rushes into the space left by the rising air. Lower pressures mean more unstable air, faster winds and a worse storm.

“We concluded that Mallory and Irvine most likely encountered a very intense storm as they made their way towards the summit.”

The once-daily air pressure measurements meant Semple and Moore couldn’t track how the storm developed during Mallory and Irvine’s climb. But Odell’s diaries say a “rather severe blizzard” began around 2pm on 8th June that lasted around two hours. Odell climbed high on Everest looking for Mallory and Irvine and wrote the winds persisted until the 10th.

Semple and Moore think the storm was a Western Disturbance – a weather system responsible for most of the severe weather and thunderstorms occurring outside Asia’s monsoon season. The Indian Meteorological Society map for 9th June shows a storm system over north central India, which brought up to 170mm of rain to the region in 24 hours. Warm air moved northwards towards the Himalayas ahead of the storm. Semple and Moore says this would explain why temperatures at Base Camp rose in the hours before Mallory and Irvine set off to the summit.

Once on the ascent to the summit, the falling air pressure and storm would have placed Mallory and Irvine in terrible danger. Falling air pressure reduces the amount of air, including oxygen, available to breathe, increasing the symptoms of hypoxia – oxygen deficiency – the climbers would already have been suffering in the death zone. “Mount Everest is so high that the low barometric pressure near its summit places humans extremely close to the tolerance limit for hypoxia; changes in pressure near the summit as small as four millibars have been argued to be of physiological relevance”, Semple and Moore say in their paper.

They explain what could have happened next. “Compounded by the cumulative effects of hypoxia, fatigue and extreme cold, Mallory and Irvine would have been at the limit of their endurance as they moved along the Northeast Ridge of Everest in the midst of a severe blizzard… Their situation would have been aggravated by the fact they most likely ran out of supplemental oxygen early on the afternoon of 8th”.

“Cognitive impairment during descent brought on by hypoxia is the most common cause of death on Mount Everest. Although the details of what happened to Mallory and Irvine are still not fully known, we believe that there is compelling evidence… that the weather during their summit attempt may have been more severe than previously thought”.

Semple – an experienced climber – and Moore think their findings will help modern-day climbers stay alive on Everest and other deadly peaks.

This story is also in this morning’s Telegraph and on BBC News.