Alaska Volcano Observatory

From McGimsey and others (2014): "On March 18 and 19, 2009, local Copper River Basin residents observed a large, unusual cloud emanating from the summit of Mount Sanford volcano (figs. 2-4). AVO was alerted on March 19 because the cloud had persisted for more than 24 hours and some residents were concerned that the cloud indicated volcanic activity. The cloud was reported to extend for more than 50 km (30 mi). The plume was visible March 19 on a webcam located at the High Frequency Active Auroral Research Program (HAARP) facility, 29 km (18 mi) north of Glennallen, Alaska, but the view was 'all clear' at Sanford from this camera on March 20. From the vantage point of most residents of the Copper River Basin, this cloud appeared to be a feature unique to Sanford; however, AVO remote sensing specialists examining satellite images of the region reported that this was one of several orographic clouds streaming off the higher mountain peaks in the area. AVO issued an Information Statement on March 20 to report and explain the observations."