The fatal Ramsay Glacier rockfall of 9 November 2002

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McSaveney, M.J.; Davies, T.R.; Ashby, G.L. 2003 The fatal Ramsay Glacier rockfall of 9 November 2002 . Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 2003/02 17 p.

Abstract: Recession of Ramsay Glacier since the late 19th Century has formed a proglacial lake at the glacier terminus in the headwaters of Rakaia River, Canterbury. The lake is flanked to east and west by high, steep walls of unconsolidated, bouldery, glacial moraine. The lake shore comprises screes of large boulders that have fallen from the moraine. The access route to Ramsay Glacier traverses the foot of these screes for some 700 metres along the lake shore, and users of the route are exposed to the danger of rocks falling from the moraine wall. A fall of some thousands of cubic metres of bouldery gravel while two trampers were traversing the route on the afternoon of 9 November 2002, killed Simon Raymond Hassall, 26. His companion who was a few metres ahead of him escaped unscathed. At the time of the accident, they had all but completed their traverse along the foot of the unstable moraine wall, which they had traversed an hour or so earlier in the opposite direction without incident. Mr Hassall had alerted his colleague to watch for rockfalls only minutes before the pair saw a huge piece of debris detach from the top of the moraine wall 270 metres above them. The detached mass contained many large boulders, with hundreds being several metres and more across. Mr Duggan reached safety. One or more boulder fragments fatally injured Mr Hassall and knocked him into the lake. It is likely that the rock that struck him weighed several tonnes and was travelling in excess of 150 kilometres per hour. Technically, the process of collapse of the glacial moraine wall is called dry ravelling, and the collapse itself was a very rapid, dry, debris fall. This collapse was on such a large scale, and with such large boulders, that it behaved exactly as would a large rockfall. Enormous boulders hopped and skipped down the slope, emitting huge shards of fractured rock as they hit other rocks. It is remarkable that Mr Duggan escaped the flying rocks without injury as large rock fragments sprayed up to 40 metres beyond the foot of the slope. His escape indicates that Mr Hassall possibly was only a few seconds from safety when he was hit. The event was not something that they could have outrun. The rockfall danger was recognised by the deceased, likely because he saw the evidence of shattered large boulders that they were walking among. Although he could see the sizes of fallen boulders, he was unlikely yo have been aware of how many might fall at once, or that the likelihood of rockfalls had been increased by recent wetting of the moraine wall by rain. The pair entered the valley to obtain a long-range weather forecast, taking advantage of cell-phone reception at higher altitude in the Ramsay area. There is no practical alternative to this dangerous route, but users should be made aware that they use it at their own risk, and that it is more dangerous during and shortly after rain. (auth)