BEST APRIL FOOL'S JOKE:
In Alaska, a dormant volcano started smoking. Planes were sent up. Found: ring of old tires set on fire, big sign in the middle, "April Fools!"
April Fool's Day, 1974
The Eruption of Mount Edgecumbe
Residents of Sitka, Alaska were alarmed when the long-dormant volcano neighboring them, Mount Edgecumbe, suddenly began to belch out billows of black smoke. Did this mean that the volcano was active again and would soon erupt? Terrified residents spilled out of their homes onto the streets to gaze up at the volcano, and calls poured into the local authorities.
Luckily it turned out that man, not nature, was responsible for the smoke. A local prankster named Porky Bickar had flown hundreds of old tires into the volcano's crater and then lit them on fire, all in a (successful) attempt to fool the city dwellers into believing that the volcano was stirring to life. Six years later when Mount St. Helens erupted a Sitka resident wrote to Bickar to tell him, "This time you've gone too far!"
http://www.museumofhoaxes.com/af_1974.html