I was just looking at the Alsek valley on Google Earth the other day. It's (obviously) a water-level route from behind the mountains to the coast, and abuts the

I was just looking at the Alsek valley on Google Earth the other day. It's (obviously) a water-level route from behind the mountains to the coast, and abuts the drainage divide with the Yukon. The entire Alsek-Tatshenshini-Kaskawulsh-Dezadeash system's upper reaches occur in glacier-scoured valleys so ice damming or stream undercutting could greatly change the direction rivers flow. The northwest-southeast trench that includes Kluane Lake and continues beyond Haines Junction is the Shakwak Trench [4], created by the Denali fault. Here's a map of the article's glacier and the surrounding area: http://i.imgur.com/tL84Bd0.jpg http://i.imgur.com/tL84Bd0.jpg (edited from the park map [1]) A different scan from a 1985 topo map: http://i.imgur.com/cVmWLlP.jpg http://i.imgur.com/cVmWLlP.jpg (cropped from [2]) Meanwhile, 90 kilometers downriver (south) along the Kaskawulsh->Alsek, the west-to-east Lowell Glacier used to squish the north-to-south Alsek River against the far valley wall, damming it and causing a lake to extend upstream [3]-- the last time this happened was around 1850; the source estimates it'd take a year of being dammed for lake to extend up the Dezadeash to Haines Junction. [1] http://www.pc.gc.ca/en/pn-np/yt/kluane/visit/~/media/088B38E3A3D14CECA4035A16E0CEB0B7.ashx http://www.pc.gc.ca/en/pn-np/yt/kluane/visit/~/media/088B38E... [2] http://www.canmaps.com/topo/nts250/med/115b.htm http://www.canmaps.com/topo/nts250/med/115b.htm [3] http://www.geology.gov.yk.ca/lowell_glacier.html http://www.geology.gov.yk.ca/lowell_glacier.html [4] https://en.wikipedia.org/wiki/Geography_of_Yukon#Physical_geography https://en.wikipedia.org/wiki/Geography_of_Yukon#Physical_ge...