| Note: | 03/17/1973
As should be expected the minor play of Ledge will be come more frequent as the time of eruption is approached. Those of Ledge show an interesting pattern with regard to intervals, strength, and behavior. Virtually all of the minor plays are announced with a loud puff or roar of steam from the southeastern vents for the early plays, from the middle vent and two small fumerole vents for the middle minor plays and from possibly all the vents in the later plays just before the eruption. Usually each minor play starts near the southeastern vents & rapidly spreads northwesterly toward the main vent.
Throughout the middle to late periods of minor play both internal (weaker) and external surges from either the main vent or middle vent were observed in the following action:
9:00 PM: 100 minor plays observed over 26 minute period
average interval ¾ minute. Of those, 20 were external from the main vent but interval between each external surge was irregular.
10:00 PM: exact same number and intervals of play as before, except that some of the external plays were shooting from both the main and second (middle) vents.
1100 pm 100 minor plays observed over 30 minutes, 25 were external
1130 PM 125 minor plays observed over 30 minutes, 45 were external
12 midnight 25 minor plays observed over 10 minutes, 13 were external
After midnight, some of the external surges from the main vent were very heavy, involving many gallons of water and occurring in groups. In addition, others shot tall (>10 feet) vertical jets of water from the middle vent. It appeared certain that Ledge was going to erupt in a very short time. However due to the fact that it was late and because my feet were past the point of being numb from cold, observations were terminated at 12:15 am. A reasonable estimate for the time of eruption was between 1215 and 100 am. |
