Hi Greg - Were you able to take a picture? Iliamna's steep slopes mean it has frequent avalanches and debris avalanches - so you might have been looking at a new or old slide. We have some summer photos of Iliamna's south flank - did the south face look like this? http://www.avo.alaska.edu/images/image.php?id=43261 http://www.avo.alaska.edu/images/image.php?id=46531 http://www.avo.alaska.edu/images/image.php?id=46491 Thank you for the observations - I passed them on to AVO seismologists, also. Cheryl Cameron -------- Greg Johnson wrote: I am a commercial pilot of 30 years flying in Alaska. Last night 07/19/2015 while flying over Mt Illiamna I noticed what appeared to by a extremely large mud or rock flow originating high on the Southern slope of Mt Illiamna and flowing several miles down a valley on its southern flank. The flow appeared to cover the valley in several hundreds of feet of material. It may be old but it was not covered by snow as all other areas at the same elevation are and it is something have never observed during 100s of flight over Mt Illiamna. -- Cheryl Cameron Geologist, Alaska Volcano Observatory Alaska Division of Geological & Geophysical Surveys voice: 907-451-5012 fax: 907-451-5050