Hello Monte - Thank you very much for your observations - they are helpful to us. Thank you again, Cheryl -------- Monte Gates wrote: Just flew over Veniaminof. Low level ash cloud. Noticed unusual shock wave pattern repeating at regular intervals 10-20sec apart. Never seen shock waves in ash like that even with Pavlof. You are welcome to call me at 907-830-5873 if you are interested in further info. -- Cheryl Cameron Geologist, Alaska Volcano Observatory Alaska Division of Geological & Geophysical Surveys voice: 907-451-5012 fax: 907-451-5050