March 10 – Ice, Ice, Baby

Today’s factismal: As a glacier melts, it makes sounds that are louder than a chainsaw.

Though landlubbers may think of the ocean as being silent, seafarers know the truth. As early skin-divers and scuba explorers discovered, the ocean is full of sounds ranging from the continual grinding of parrot fish jaws as they eat the coral reefs around them to the throbbing booms made by drum fish as they beat their swim bladder with their abdominal muscles. And perhaps the best known example of ocean sounds are the various calls of the whales, from the friendly bottlenose dolphin’s whistles and clicks as it searches for food to the blue whale’s explosive shouts that cover half the ocean.

This parrot fish is actually pretty noisy (My camera)

This parrot fish is actually pretty noisy
(My camera)

It isn’t only critters that make noise in the water. Volcanic eruptions from the mid-Atlantic ridge and mid-Pacific seamounts hiss and sputter as the hot rock is suddenly quenched by the ice-cold water. Landslides along the continental shelves rumble threateningly as they dump tons of sediment and nutrients into the benthic ocean. Earthquakes fill the water column with a rolling thunder. And, surprisingly, even the glaciers add their soupçon of susurrus to the mix. You see, glaciers are formed when snow piles up faster than it can melt. As the snow piles higher and higher, it squeezes the individual snowflakes into a solid mass of ice. During the process, most of the air is squeezed out, but small bubbles can get trapped.

This is where the glacier meets the sea (My camera)

This is where the glacier meets the sea
(My camera)

If the glacier is on a slope that heads down toward the ocean, it will slide downhill and create what is known as a tidewater glacier. The weight of the ice mass up high in the mountains pushes the glacier oh so slowly out into the water, where it breaks off in bits. But, because the water is slightly warmer than the glacier, the ice at the bottom of the glacier melts. As it melts, it releases those air bubbles that were trapped so long ago. And those suddenly freed bubbles spring into a near-perfect sphere with a sudden “gloing!” of freedom. When enough of those bubbles pop open, it creates a 120 dB ruckus that is louder than a chainsaw!

A glacier calving; this isn't the noisy part! (My camera)

A glacier calving; this isn’t the noisy part!
(My camera)

Now the interesting thing about that sound is that it isn’t all bad. Seals and sea lions like to dive near glaciers, looking for fish to eat. And orcas like to dive near the seals and sea lions, looking for something to eat. But where seals use their eyes and whiskers to search for food, orcas use sound; like other whales, they send out a sonar beam that gets reflected off of things nearby helping the orca to locate a likely snack. But the constant noise of the glaciers makes it hard for the orcas to hear the reflected sound of their sonar; like someone trying to whisper in a rock concert, it just doesn’t work very well.

An orca's favorite snack (My camera)

An orca’s favorite snack
(My camera)

If you’d like to learn more about how orcas use sound to track their prey (and maybe even use the orcas’ own sounds to track them!), swim over to Orcasound.net:
http://www.orcasound.net/

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