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It was announced this week that Victor Vescovo drove solo to 35,853 feet to the bottom of Challenger Deep in the Marianas Trench off the coast of Japan in a submersible named “The Limiting Factor” in April.

The pressures at this depth are immense and here is why.

When I go into a classroom and talk about pressure, it’s often difficult for many younger students to get a good grasp on the subject. But when it comes to weather forecasting, air pressure is one of the most important factors.

Imagine a 1-square-inch column of air measured from the top of the atmosphere down to sea level. It would weigh about 14.7 pounds. This pressure, or weight of the air, is caused by gravity pulling the atmosphere toward Earth.

Earth’s atmosphere becomes lighter with altitude. Half of the atmosphere’s weight lies between Earth’s surface and an altitude of about 18,000 feet.

We can see the effect of this by observing the temperature at which water boils. Water will boil at 212 degrees Fahrenheit (100 degrees Celsius) at sea level but will boil at much lower temperatures as you go up in altitude because of less air pressure. Therefore, baking at higher elevations often requires modifications to a recipe.

Usually you don’t really notice this pressure because it’s being applied to you from all directions, but quick changes in altitude can affect your body. One local example in altitude change occurs when driving over the Sierra Nevada mountains - you will feel your ears pop as you increase in altitude.

This is caused by your inner ear trying to equalize with the outside air pressure. Another example is when you fly across the country in a jetliner about 32,000 feet — the outside air pressure is about 4.3 pounds per square inch.

But the pressure gets greater as you get closer to sea level and beyond. When scuba diving in the ocean, you only need to go down about 33 feet to reach another 14.7 pounds of pressure, or one atmosphere. The ocean’s greatest depth is the Marianas Trench in the western Pacific near Guam. The ocean bottom is more than 36,000 feet below sea level, or about 20 percent deeper than Mount Everest is high. The pressure at this depth is astounding, surpassing 16,000 pounds per square inch. Imagine a linoleum square sitting on the bottom of that trench that measured one square foot; the water column above it would weigh more than 1,100 tons.

Despite this tremendous amount of pressure, U.S. Navy Lt. Donald Walsh and Swiss explorer Jacques Piccard took the deep-diving submarine Trieste to the bottom of Challenger Deep in the Marianas Trench in 1960. It was an amazing feat then, and still today.

John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative. Email him at pgeweather@pge.com or follow him on Twitter @PGE_John.

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