Three distinct phenomena related to sudden lake drainage, which occurred in a restricted area within the southern Coast Mountains of British Columbia, are described: (i) moraine breaching by solitary wave action following an icefall into a lake; (ii) failure of a glacier ice dam by flotation and melting to produce a ‘glacier outburst’ flood or ‘jökulhlaup;’ (iii) debris torrent following a moraine breach. The possibility for a fourth failure phenomenon: moraine failure by piping, is discussed. A first attempt to develop practical hazard evaluation methods before the event, which relies on simple scale relations or index relations developed from experience of events elsewhere, is presented. Key words: dam break, debris flow, hazard evaluation, jökulhlaup, lakes, lake drainage.