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No matter how closely you listen, you will not hear the Earth hum—but humming it is.No matter how closely you listen, you will not hear the Earth hum—but humming it is.
Far, far below the range of human hearing, waves of energy are coursing through the crust, causing the ground beneath your feet to rise and fall about three-millionths of an inch every few minutes. First detected by networks monitoring seismic activity in 1998, the tiny ripples were initially chalked up to the many small earthquakes that occur each day around the world. But studies over the past decade have proved that the hum is far too constant for that explanation.
In February, oceanographer-turned-seismologist Spahr Webb, of Columbia University’s Lamont-Doherty Earth Observatory, reported finding the hum’s likely origin: ocean waves colliding over continental shelves. When two trains of waves, traveling in different directions, smash into one another, they send a continuous cacophony down to the seafloor. That energy triggers vibrations that ripple through the planet, producing an inaudible ringing. “It’s the equivalent of a magnitude 6 earthquake occurring every day,” Webb says. “That’s the kind of energy we’re talking about.”
Earth’s hum turns out to be just one of the many enigmatic signals resonating in the range known as infrasound. Broadly defined as sound waves longer than 56 feet, infrasound lies below the rumbling 20-hertz bass notes at the threshold of human hearing. Hurricanes, tsunamis, and tornadoes also generate their own characteristic low-frequency noise. Scientists are now studying infrasound to learn more about those powerful natural events and how to predict them—a skill that certain animals may already have. In fact, some animals generate their own ultrabass tones for a unique type of long-distance communication.
A spectrogram of ocean sounds
records a tremor from an underwater
volcano near Japan. Each column represents a
three-minute pulse of an ultralow sound.
Maps from previous missions showed only a bump on the seafloor about 200 miles west of Grays Harbor. But the contours of a large volcano emerged as sonar mapped the ocean floor more than 10,000 feet below the surface.
TeThe ocean's floor hasn't been mapped in great detail along much of Washington's coast, making it a worthwhile place to test the sonar technology, Weirich said. The high-resolution sonar mapped each depth as a different color, showing a dynamic ocean floor with deep ridges and canyonsxt
Geologists recently announced that there might be more things that Mount St. Helens, Mount Rainier and Mount Adams have in common, other than the fact that they are all volcanoes. Preliminary studies seem to indicate that they draw their lava from the same enormous magma pool that spans the entire southwestern portion of Washington state. The science team that conducted the investigation revealed in the October 25 issue of the journal Nature Geoscience that the setup in Washington might be similar to the one known to exist under the Yellowstone supervolcano, LiveScience reports.