Scuba diving Part IV: The Scientific Method and Infrasonic Warning: "Hey, Mitch is on His Way!"

The Scientific Method and Warnings of Hurricane Mitch


The Webster's® Dictionary defines infrasonic, or infrasound, 
as "1: having or relating to a frequency below the audibility range of the human ear; and 2: utilizing or produced by infrasonic waves or vibrations."

Infrasound emitted by earthquakes, pounding surf, waterfalls, calving of glacial ice, tidal waves, aurora borealis (0.1 - 0.01 Hz), solar flares, solar winds, hurricanes, thunderstorms, the jet stream (30-40Hz), and winds in caverns (20-30 Hz.), effects non-human wildlife and causes natural, instinctive reactions to the acoustics produced by these environmental events. Low-frequency noise (LFN) typically causes animals to flee, hide, or take other protective measures.

The otolithic organs in fish react to a broad range of frequencies, especially infrasonic warnings occurring from a category 5 hurricane (Saffir–Simpson Hurricane Scale) approaching a day away. Although I am neither a meteorologist or ichthyologist, nor an ichthyologist who would hypothecate about the meteorological effect of a hurricane on fish, I know for sure that this phenomenon exists, and I witnessed it on the barrier reef bordering Belize on October 25, 1998.

Fancy science often gets in the way of common sense. The scientific method is a simple step-by-step process that can be followed naturally, even by non-scientists. If you can remember back to high school it starts with the problem. For my dive partner and me it began on the morning of October 25, 1998 as we walked out to the dive shop on a rustic dock on Ambergris Caye in Belize. Carrie looked at a color weather map printed off an inkjet printer pinned to the back door of the little shack. “What’s that map showing there?” she asked innocently. “Oh, that?” one of the hearty, tanned employees replied sheepishly. “Just a little old picture of the forecast path of Hurricane Mitch, which is category 5 (Saffir–Simpson Hurricane Scale) btw, and headed this direction in a couple of days!” [not really, the answer was vague]. The first part of the scientific method is to find out exactly what it is you want to learn? We were curious about a map but the bigger questions should have been about the track and effect of Hurricane Mitch. Strike one and strike two.

As eager divers with one last dive left on our schedule that Sunday morning, we went below the surface to observe the beautiful undersea world we spent the week exploring. The second important step in the scientific method is observation. What we saw or did not see as the case may be, was the total absence of wildlife. Like the lonely sheriff, walking deserted streets before the Hole-in-the-Wall gang hits town, all the usual suspects were gone; no shark, snapper, reef fish, trigger-fish, nobody.

The dive plan was to hunt up some lobster and bake them on the beach but we decided to come back to the surface because all the lobster had left town. My distinct, scientific recollection was that all wildlife was absent in a world teaming with them just days before; and upon arriving back at the dock, our observation of this phenomenon produced a lively discussion at the dive shack. Now the radar tracking map from the WeatherChannel© seemed strikingly relevant! We observed the story as eyewitnesses.

Nature’s suggestion for the next step in our scientific road to discovery was that “something was up!” Divers are used to the dearth of sound from the environment under water; however the absence of life was insurmountably strange. The supposition that we missed an important warning made me feel like a banana that was past ripeness and starting to stink. Threatening infrasonic warnings issued to the fish and even to the divers were heeded or not, but it did not change the facts: one of the largest hurricanes in history was headed for our island paradise on a collision course with death.

Predictions of what came next flew around the island that evening as we packed to leave the next day. We helped the bartenders pack their hut and in the morning nailed plywood to the windows of the hotel; meanwhile the tracking map showed Hurricane Mitch poised to strike Belize in a couple of days. The turning point in the storm was the next day October 26, 1998, when it reached its strongest peak in pressure, speed, and force; as we waited helplessly at the small airport, along with everyone else on the island trying to leave Ambergris Caye. This category of hurricane is doubtless deadly and by Monday we were terrified.

The hypothesis that the undersea world was properly informed of the danger of Hurricane Mitch by LFN played out before our eyes that ominous day in 1998. We observed something in nature totally unusual, and concluded that there was an important reason the fish were gone. The prediction of impending disaster became critically serious once we studied the weather map and listened to the discussion about Hurricane Mitch later that day.

Hurricane Mitch (Satellite view 1998)

Fortunately we escaped the hurricane’s wrath, not having to test our scientific hypothesis; it made a precipitous turn south, narrowly avoiding the chain of islands. But for as long as I am a diver, I will never forget the day the fish were completely absent when they heard Mitch was coming. What happened to Honduras is testament to the power of this storm: unofficial reports totaled the rainfall in Honduras during this storm at 75 inches, and it was the deadliest Atlantic hurricane since 1780 (218 years).

©Mark H. Pillsbury