Great Expectations: Different High-Risk Activities Satisfy Different Motives.

This article has some great quotes in the intro and some interesting perspectives on what motivates mountaineers to get out and challenge themselves and how it is different from typical "thrill-seekers." 

http://www.ncbi.nlm.nih.gov/pubmed/?term=Great+Expectations%3A+Different+High-Risk+Activities+Satisfy+Different+Motives. 

The attraction of the high-risk domain is that it enables participants to move from a nonspecific, ambiguous, and internal anxiety to a specific, identifiable, and externally derived intense emotion: fear (cf. Castanier, Le Scanff, & Woodman, 2011; Fenichel, 1939).