WEATHER AND DEATH ON MOUNT EVEREST An Analysis of the Into Thin Air Storm BY G. W. K. MOORE AND JOHJ N L. SEMPLE A reconstruction of the meteorological condition leading to the deadly 1996 storm suggests promise for improving the predictability of mountain weather hazards and raises caution about the dangers of stratospheric ozone intrusions. ith a height of8,848 m, Mount Everest is the highest mountain in the world. For over a century, it has been the subject of Wexploration for both scientific and recreational purposes ABOVE. Clouds approach the (Venables 2003). This exploration began in earnest with the British ex- Tibetan (north) side of Mount peditions during the early part of the twentieth century. At that time, Everest in the evening sun, Nepal was closed to foreigners and so these efforts were focussed on signaling a possible change in finding a route to the summit from the north through Tibet (Hemmleb the weather for the following et al. 2001; Venables 2003). During the 1921 expedition, a potential day. Storms on Everest are a route to the summit was identified that is now referred to as the North significant risk for mountaineers, appearing without warning and Col-North Ridge route (Fig. 1). It was via this route during the 1924 causing falling temperatures, expedition that Norton attained an altitude of 8,565 m without the increased winds, and heavy use of supplemental oxygen—a record that stood for 54 years until snowfall. [Photograph by J. L. Messner and Habler reached the summit in 1978 (Messner 1999; West Semple, May 2005.] 2000). Several days after Norton's feat, • AMERICAN METEOROLOGICAL SOCIETY Unauthenticated | DownloadedAPRIL 200 09/24/216 BAH5 01:25- | 46 PM5 UTC this route until the beginning of World War II. After the war, as a result of turmoil in Tibet and the opening of Nepal to foreigners, the focus of the explora- tion of Mount Everest shifted to the south and the discovery of a route that followed the large horseshoe- shaped cirque or valley known as the Western Cwm, bounded by Nuptse, Lhotse, and Everest to the South Col, and then ultimately to the summit (Venables 2003). This route, known as the South Col route (Fig. 1), as- cends through the Khumbu Glacier and Kumbu Ice Fall into the Western Cwm, up and across the Lhotse Face to the South Col, and then along the south ridge to the summit of Everest. Please refer to Fig. 2 for a three- dimensional representation of Mount Everest developed by Gruen and Murai (2002) that provides further information on this route. This route FIG. I. Image of Mount Everest taken from the space shuttle I Oct was the one used by Hillary and 1993. In this striking early morning image, the north and south faces of Mount Everest as well as the Western Cwm, the large cirque to the Norgay (Hillary 2003) in the first west of Mount Everest, are in shadows while the Kangshung, or eastern, successful summit of Mount Everest face, is in bright sunlight. The South Col is situated between the sum- in May 1953. Although other routes mit of Everest and Lhotse, while the North Col is situated between the to the summit have been pioneered summit and Bei (or Changtse). Typical climbing routes via the South in the intervening years, these two and North Col are indicated. [NASA photograph STS058-I0I-I2.] routes remain the most popular (Huey and Salisbury 2003). Mallory and Irvine perished during a summit at- Much of the focus of scientific interest in Mount tempt made with the use of supplemental oxygen Everest has been on the impact that the low barometric (Hemmleb et al. 2001; Venables 2003). To this day, pressure near its summit has on human physiology it is still unclear if Mallory and Irvine were able to (Houston et al. 1987; West 1999; Huey and Eguskitza reach the summit before their deaths (Hemmleb 2001). These studies have shown that above 7,000 m, et al. 2001; Messner and Carruthers 2001; Hemmleb climbers are at the limits of their endurance and are et al. 2002). Exploration of Everest continued via exposed to significant risks associated with the reduced amount of oxygen available for respiration: cold tem- peratures and high winds (West et al. 1983a; West 2000; AFFILIATIONS: MOORE—Department of Physics, University Huey and Eguskitza 2001; Huey et al. 2001). of Toronto, Toronto, Ontario, Canada; SEMPLE—Department of Perhaps the most dramatic example of these risks Surgery, University of Toronto, Toronto, Ontario, Canada CORRESPONDING AUTHOR: Prof. G. W. K. Moore, occurred in early May 1996 when a storm engulfed Department of Physics, University of Toronto, 60 George Street, Mount Everest, trapping a number of climbers on Toronto ON M5S IA7, Canada. its exposed upper slopes and ultimately resulting E-mail: [email protected] in eight deaths.1 This event and the ensuing tragedy The abstract for this article can be found in this issue, following the 1 table of contents. It has become conventional to refer to this event as a "storm," DOI: 10.1175/BAMS-87-4-465 although as we shall show it was in all likelihood an extended In final form 11 October 2005 outbreak of unfavorable weather with two distinct periods ©2006 American Meteorological Society of very stormy weather. For simplicity, we will refer to the event as the Into Thin Air storm. 466 I BAflS- APRIL 2006 Unauthenticated | Downloaded 09/24/21 01:25 PM UTC received international attention at the time (Burns 1996; Horsnell and Faux 1996) and became the subject of a number of books, including Into Thin Air (Krakauer 1999) and others (Boukreev and DeWalt 1999; Breashears 1999; Dickinson 1999), as well as figuring prominently in the movie "Everest" (MacGillvray and Breashears 1998). On the evening of 9 May 1996,2 a large number of climbers were poised to make summit attempts from camp IV situated at 8,000 m on the South Col of Mount Everest (Fig. 2). High winds had persisted throughout the day and the pos- sibility of summitting appeared low. The winds died down during the evening and the conventional wisdom was that they would remain calm for a period of time. As a result, FIG. 2. Three-dimensional photorealistic visualization of Mount the decision was made to attempt to Everest showing features and approximate elevations along the South summit and the climbers left around Col route. Visualization courtesy of A. Gruen, Institute of Geodesy 2000 LT on the 9th for the 18-24-h and Photogrammetry, Swiss Federal Institute of Technology. round-trip to the summit. During the afternoon of 10 May, an intense storm3 with wind that had taken shelter were suffering from the lack speeds estimated to be in excess of 30 m s_1, heavy of oxygen that, as will be discussed in this paper, snowfall, and falling temperatures engulfed Mount may have been exacerbated by the unusually low Everest, trapping over 20 climbers on the exposed barometric pressure. A number of climbing parties upper sections of the mountain above the South Col who were attempting to summit along the North (Fig. 2). The unfavorable weather appears to have Col-North Ridge route (Fig. 1) were also trapped by abated overnight, although winds remained high near the storm and three people died. Although the harsh the summit. There was however a reintensification weather abated after the 11th, winds near the summit during the day on the 11th. Throughout this period, remained high for next 5 days, hindering attempts a number of heroic attempts were undertaken to res- to summit. cue the trapped climbers that were hampered by the In Fig. 3, infrared imagery from the National high winds and the harsh weather. Tragically, five of Oceanic and Atmospheric Administration (NOAA) the climbers could not be rescued and perished. By family of polar-orbiting satellites are presented for the afternoon of the 11th, most of the people on the the late afternoon during the period of 9-12 May upper slopes of Mount Everest were sheltered in tents 1996. The images are derived from the Global Area at the South Col (Fig. 2). In this regard, the impact Coverage (GAC) level-IB dataset (Kidwell 1998) and of the weather on the 11th was not as catastrophic as have a resolution of 4 km. Brightness temperatures that on the 10th. Supplemental oxygen was however derived from the observed radiances are presented in short supply and there is evidence that even those with a color map in which colder (and therefore 2 The following narrative is based on the published recollections of the storm as contained in Boukreev and DeWalt (1999), Dickinson (1999), and Krakauer (1999). All times are given in local Nepalese time, which is 5 h and 45 min ahead of coordi- nated universal time. 3 Among those on the upper slopes of Everest was a pilot who was familiar with the appearance of thunderstorms as seen from above. He is quoted in Krakauer (1999) as stating that he believed that the clouds that engulfed Mount Everest were associated with the crown of a "robust" thunderstorm. In two separate incidents during the storm, Krakauer (1999) reports that he and a sherpa observed thunder and lightning. AMERICAN METEOROLOGICAL SOCIETY APRIL 2006 BAF15- | 467 Unauthenticated | Downloaded 09/24/21 01:25 PM UTC activity in the vicinity of Mount Everest. This outbreak of high- impact weather resulted in the largest number of fatalities (8) to occur near the summit of Everest dur- ing a single event. In the ensuing years, a passionate and wide-ranging debate has been ongoing in an attempt to understand the factors that contributed to this tragedy (Boukreev and DeWalt 1999; Breashears 1999; Dickinson 1999; Krakauer 1999; Roberto 2002; Mangione 2003; Kayes 2004).