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Mount Cleveland, Alaska (52Њ49ЈN, 169Њ57ЈW), located on Chuginadak Island, erupted on 19 February 2001. The atmosphere-volcanic plume interactions that occurred as part of this event led to several serious encounters of commercial aircraft with the ash. A number of continental and oceanic air traffic control areas were affected. Here, a detailed case study of the eruption, subsequent movement of the airborne plume, and operational response is presented. The likelihood of such encounters in the future may be reduced as a result of lessons learned from this event. Some potential new assets for improving the detection of and response to the airborne volcanic ash hazard to aviation also are discussed.

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The Hill Cipher, also known as matrix encryption, uses matrices to encipher and decipher text. Various attacks, such as those found by Jack Levine [2, 3, 5], have been published for this system. This article reviews a few previous results and presents a powerful new attack in which the rows of the matrix can be determined independent of one another, greatly reducing the amount of time needed for decipherment.