Most of us are familiar with different types of electromagnetic radiation. They’re found everywhere, from our Wi-Fi to inside microwaves to the very light that we see. Waves have properties, like frequency and wavelengths, that are measured in foreign sounding units like Ångströms, but the story goes far beyond that. As we move up the electromagnetic spectrum, past microwaves and radio waves, we enter the uncharted territories of ELF – Extremely Low Frequency Waves.
Extremely Low Frequency waves are those with a frequency from 3Hz to 30Hz. A frequency this low almost guarantees that these waves will have some quirky qualities – and they do! ELF wavelengths range from 100,000 to 10,000 kilometers in size. The earth’s diameter, in comparison, is only 12,742 kilometers (7,917.5 mi). They can propagate through almost any substance, which gives them a huge scope in terms of how far they reach. ELF waves laugh in the face of walls, trees and even giant bodies of water as they pass right through them, as though they aren’t even there. In fact, the last one, large bodies of water, gives ELF waves a rather interesting usage for those of us on the planet (or beneath the waves) – communication between submarines!
Submarines that operate in deep waters are typically unreachable through traditional radio waves, as sea water is electrically conductive, effectively shielding submarines from these higher frequency waves. However, ELF waves are able to penetrate the murky depths of the sea, so they’re used by the US, Soviet and Indian Navies to communicate with submarines. Coincidentally, the United States, Russia and India are the only countries that have developed ELF communication facilities.
There are some setbacks, however. As the transmission rate for ELF communication is really low, only a few characters can be sent at a time. Furthermore, the correspondence only goes one way, as submarines themselves cannot host transmission antennas large enough to beam ELF waves back. A typical ELF antenna can be several miles long, owing to the gigantic wavelengths and low frequencies in question. There’s actually a 28-mile long ELF antenna in Michigan! Fortunately, they’re not pointing up towards the sky; they are wires laid out along wooden poles, similar to a power line.
Transmission from these waves can be detected pretty much anywhere. ELF signals meant for Russian submarines were once picked up in Antarctica, which means that once an ELF transmission is out there, it’s really ‘out there’. The biggest problem with using this form of communication is background noise; there is a low signal-to-noise ratio, coupled with the fact that you’re only sending a few characters per minute. This means that ELF is mostly used to establish other forms of two-way communication with submarines. Essentially, it’s the Internet Explorer of electromagnetic waves.
Where Do We Find ELF Waves?
Aside from its limited man-made uses due to the difficulty of transmission, ELF waves are also created by lightning in the earth’s atmosphere. When lightning strikes, the intense burst of energy causes electrons in the earth’s atmosphere to oscillate, which gives rise to these waves. Those are pretty exciting origins for things as seemingly bland and insipid as Extremely Low Frequency waves!
Weird things start to happen at these low frequencies. One of the loudest sounds ever recorded was the famous “Bloop”, a very low frequency sound wave. In June 1997, oceanographers picked up a minute-long, low frequency ‘infrasound’ (below 20Hz and therefore undetectable by the human ear) source. They triangulated its location to about 3000 miles away from the recording, far across the Indian Ocean. Speculation quickly began about its source, with some thinking that it could have been an animal or a sea monster. The loudest known animal is the blue whale, measuring in at 188 decibels, but the “Bloop” was several times louder than that.
After almost a decade of argument and analysis, it is now widely believed that the “Bloop” was caused by breaking ice sheets in the Antarctic. In other words, one of the loudest sounds ever was literally caused by global warming. Maybe the “Bloop” was simply the sound of Earth crying…