Avalanche Accidents Causing Fatalities: Are They Any Different in the Summer?

Introduction

Most avalanche accidents occur during leisure activities in winter (Techel and Zweifel, 2013). Asphyxia from snow burial is the most common cause of death, and the prognosis for avalanche victims with unwitnessed asystolic cardiac arrest is poor (Brugger et al., 2013; Boué et al., 2014; Mair et al., 2014; Truhlar et al., 2015). Companion rescue is of utmost importance, and prehospital organized rescue teams must intervene promptly, have specific training for avalanche rescue, and carry appropriate safety and medical equipment (Brugger et al., 2013; Mair et al., 2013). Although rare, some of the most lethal recreational avalanche accidents in the European Alps occurred in summer (Jarry, 2012; Harvey et al., 2013). Most research and prevention efforts have focused primarily on winter avalanche. This study aimed to address this knowledge gap by focusing on the epidemiology of summer avalanche accidents.

Patients and Methods

We investigated avalanche accidents that occurred in Switzerland in unsecured terrain, which caused at least one fatality, from 1984 to 2014. We retrieved data from the registry of the WSL Institute for Snow and Avalanche Research SLF Davos (hereafter SLF), which prospectively collects information about all avalanche accidents in Switzerland. Accidents resulting in fatalities are systematically reported to SLF by rescue organizations and police, and the registry also includes accidents when the victim dies at a later stage in the hospital. For the vast majority of cases, the SLF is granted access to the police reports. In this study, summer was defined as the period between June 1st and October 31st. During these months, the leisure activity of accident parties is mainly dedicated to hiking and alpine climbing, whereas the winter period is mostly dedicated to backcountry touring and off-piste riding. Thus, we use a definition of summer based on the main alpine recreational activities rather than the calendar months usually considered as summer months.

The following data were collected in the registry: date of the avalanche; activity engaged when the avalanche occurred; the elevation and slope of the avalanche start zone; the slope (except for strictly east- and west-facing slopes) was categorized as north- or south-facing slopes; the avalanche path parameters, including the change in elevation between start and end zones, the distance covered, the avalanche type (slab or loose), and snow wetness (dry or wet) (EAWS, 2016). The terrain features in the avalanche path were considered as unfavorable when it consisted of single trees or forest, rock gullies or rock cliffs, single large rocks, or glacier seracs. Complete burial was defined as burial of both the head and chest (Brugger et al., 2013). The depth, duration of the burial, and the means of discovery were also collected. The presumed cause of death was recorded for most summer avalanche accidents. Trauma was assumed to be the cause of death when the victim had patent airways (not fully buried). In addition, two of the authors (M.P. and A.K.) reviewed accident descriptions for completely buried individuals and independently judged the cause of death (asphyxia, trauma, or undetermined). In cases of disagreement, the cause of death was considered “undetermined.” Data of the medical chart were available for some patients through an ethics committee-approved registry that included victims between 2013 and 2014.

Results

Summer avalanches accounted for 21 (4%) of 482 avalanches with at least one fatality occurring during the study period, and 40 (6%) of 655 fatalities attributed to avalanches. The main activity of 38 people who died was alpine climbing (95%) (38 of 40) in summer.

Summer avalanches more frequently occurred in southern-aspect start zones and at higher elevations than similar avalanches occurring in the winter (Table 1). The elevation drop and the proportion of unfavorable terrain conditions in the avalanche path were almost twice as high in summer than in winter. Avalanches were predominantly dry snow slab avalanches in winter and wet snow avalanches in summer.

The mean number of fatalities per avalanche accident involving at least one fatality was higher in summer than in winter (Table 2). The burial type was available in most cases, but the depth and duration of the burial and the means of discovery were only partially available. Ninety-one percent (557 of 614) of fatalities occurred after complete burial in winter, compared with 36% (14 of 39) in summer. In winter, among the completely buried individuals, 40% (274 of 684) were found using signals from an avalanche transceiver; 35% (237 of 684) were located by companions. In summer, all the completely buried individuals who were found were located by organized rescue teams, generally by detecting materials visible on the snow surface (65%, 10 of 16); none were detected with an avalanche transceiver.

Trauma was the cause of death in 94% (33 of 35) of summer avalanche accidents, when cause could be determined. Details of all summer avalanche accidents are presented in Table 3. Death was pronounced by the prehospital physician on site for all but one of the fatalities.

Discussion

This study was the first to present summer avalanche accidents as a distinct entity. We showed that, compared with winter, summer avalanche accidents with at least one fatality resulted in a higher mean number of fatalities per avalanche, and the deaths mostly resulted from trauma.

Several factors may have contributed to the high mean number of fatalities per avalanche. The first is the larger mean number of individuals involved per avalanche, although the numbers involved in summer and winter avalanches were not significantly different in our study. A second factor is the burial type, which was shown previously to be the strongest single factor for survival from winter avalanches (Brugger et al., 2001). As a significantly lower proportion of individuals were completely buried per avalanche accident in summer than in winter in our study, burial type, however, could not explain the high summer fatality rate. The third factor is the avalanche terrain. The main summer activity was alpine climbing, which takes place on exposed terrain, enhancing the risk of sustaining a life-threatening trauma (Hohlrieder et al., 2007). This hypothesis is a plausible explanation for our findings and is supported by the significant vertical drops and the unfavorable avalanche paths observed in most, if not all, summer avalanches.

We also found that the cause of death in summer avalanches was almost exclusively attributed to trauma, which was closely linked to summer activities. Although reliable information about the cause of death is not always available for winter avalanches, several studies have shown that avalanche deaths were mostly caused by asphyxia (Hohlrieder et al., 2007; McIntosh et al., 2007; Brugger et al., 2013; Truhlar et al., 2015). Also, two studies showed that trauma accounted for only 5.6% and 16%, respectively, of fatalities from avalanche accidents in a population and setting comparable to ours, in the European Alps (Hohlrieder et al., 2007; Moroder et al., 2015).

Our findings have some potentially important practical implications. Although infrequent, summer avalanches accounted for about 6% of fatalities associated with avalanches. Therefore, as repeatedly emphasized, mountaineers should include avalanche danger in their risk management for summer outings (Harvey et al., 2012; ICAR, 2015). Indeed, a careful evaluation of the avalanche situations in summer is as necessary as in winter because even small avalanches may result in falls, which can cause severe injuries.

In summer avalanche accidents, and particularly in those where people experience falls over a great height and/or unfavorable terrain, rapid response by medical teams is of utmost importance. This is in contrast to winter avalanche accidents, when companion rescue is extremely important (Hohlrieder et al., 2005; Mair et al., 2013). Two reasons may explain these differences: first, in summer, severe traumatic injuries are more frequent than full burial, and hence rapid extraction by companions is often of lesser importance than rapid administering of first aid by response teams. Second, the location of the victim is often only accessible by helicopter, as frequently very steep and exposed terrain (Table 1) make the access to the avalanche run-out zone very time consuming and dangerous.

Some important implications for organized rescue teams also emerged from our findings. First, the high mean elevation of summer avalanche accidents—coupled with the high summer temperatures—will negatively impact helicopter performance. This may become crucial, including if winching procedures are required, which is not uncommon in avalanche rescues (Hohlrieder et al., 2007; Pasquier et al., 2012). Second, in contrast to winter fatalities, we found that trauma was the predominant cause of death; this finding may also have potentially important consequences in medical management. Traumatic cardiac arrest indeed requires specific treatment, which would support early dispatch to the avalanche site of rescue teams trained in advance trauma care in difficult terrain (Mair et al., 2013; Truhlar et al., 2015). Finally, we found that a large proportion of these avalanche accidents involved multiple casualties. Although this scenario is not specific to summer accidents, the rescue operation should be prepared to send extra resources and provide on-site triage (Bogle et al., 2010; Mair et al., 2013; Truhlar et al., 2015).

Our study has some limitations. First, we included only avalanche accidents with at least one fatality that occurred in unsecured terrain. This subset only represented 10%–15% of all reported avalanche accidents in Switzerland (Techel et al., 2015). These strict selection criteria must be considered when comparing our results to results based on all reported avalanche accidents, particularly mortality rates among individuals completely buried. However, as shown by Techel and Zweifel (2013), the reporting rate of avalanche accidents depends on the severity of the accident, and varies over time and region. Therefore, limiting the analysis to the dataset of accidents, which can be considered complete, are generally well investigated, and documented reduced bias in time. We applied the same criteria to summer and winter avalanche accidents; thus, comparisons made between these two groups were valid. Another limitation was the reliability of the cause of death. The database we analyzed cannot be considered a medical registry. However, fatal avalanche accidents are consistently investigated in depth, and they are generally documented by police and rescue services; thus, a detailed description of each avalanche accident was nearly always available (Techel and Zweifel, 2013). This recurrent problem in avalanche research has, however, been addressed as best as possible for the 14 completely buried fatalities. Furthermore, in our pragmatic approach, the cause of death was considered traumatic for the 63% (25 of 40) fatalities that were not or partially buried, which is consistent with other studies (Moroder et al., 2015). Finally, the small number of summer avalanche accidents included in this study may have led to spurious findings; thus, our results must be confirmed in other registries.

Conclusions

Fatal avalanche accidents that occur in summer have specific characteristics. Some of these, notably the higher mean number of fatalities per avalanche and the predominance of trauma as the cause of death, pose specific logistic and operational challenges for the rescuers. The involved rescue teams and rescue systems should be trained, prepared, and equipped adequately for these specific features to ensure safe and efficient patient care.