May 18 1980 Mt. St. Helens Eruption From 140 Miles Away.wav

This is a truly unique recording. Several years ago I found out that I am the only person in the world who captured audio of the May 18, 1980 eruption of Mt. St. Helens, the volcano in Washington state. I was in high school in 1980, living in Newport, Oregon, 140 miles southwest of the mountain. May 18 was a beautiful sunny morning, and as we were eating breakfast we heard several distant "thuds" or booms. We went outside, and noticed that they were coming from the north. We had no idea what they were, and since Mt. St. Helens was so far away, we "knew" it could not be the mountain. But in the back of my mind I thought, "could it be?". So I grabbed a tape recorder and set it in a window box upstairs on the north side of the house. This recording is an excerpt of what I captured. The entire tape is about eight minutes long. Unfortunately the quality is poor, but it was the only tape recorder we owned. I started recording about two minutes after we heard the first boom. In total there were about 10 booms over a period of about ten minutes. I never did anything with the tape because of the poor quality. Also I figured that the USGS, etc. had also recorded the sound. But I found out recently that no one else made an audio recording. The booms were picked up on seismometers, but no audio was recorded. As I understand it, when the mountain first erupted it sent a low-frequency "shock wave" straight up. This wave reflected off several layers of the atmosphere, bouncing back to the ground in a large donut-shaped ring about 50 to 300 miles around the mountain. People within 50 miles of the mountain did not hear anything. I am not sure if what we heard was one "shock wave" reflected many times between layers of the atmosphere and the ground, or a series of waves. The booms are very low frequency, thus you should listen with headphones or larger speakers. On laptop speakers you probably won't hear anything. Many people who heard the booms described them as a series of "thuds". I also believe that this may be the only audio recording of this phenomena from any volcano. I imagine that the eruption of Krakatoa in 1883 sounded similar to this (but louder). I wonder too if anyone knows of any atmospheric audio recorded from a distance greater than this (140 miles/225 km)? If you would like to study the entire recording, please contact me.

UPDATE 6/8/2014: I have uploaded the original, untouched recording here: http://www.freesound.org/people/daveincamas/sounds/240257/