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Alan Stahler: Hurricanes and earthquakes

The volcano Popocatépetl (poe-poe-kah-TEH-pet), southeast of Mexico City, grows as the floor of the Pacific collides with — and dives under — mainland Mexico.
Comisión Mexicana de Filmaciones/Creative commons |

Putting food in the oven is like strumming a guitar with a gazillion strings — heat makes the tiny particles in the food — atoms and molecules — vibrate faster. The hotter they get, the faster they shake.

When atoms and molecules vibrate, they slam into each other, push each other away. The faster they vibrate — the higher the temperature — the harder they collide, and the harder they push. Heating things up makes them expand.

Warm the air and the air expands. When air expands, it becomes less dense — a gallon of warm air holds fewer molecules than a gallon of cold air.



If the air near the ground is warmer than the air above — if the air near the ground is less dense than the air above — the warm air will float upward — warm air rises.

When really large stars runs out of fuel, it explodes, briefly giving off as much energy as all the stars in its galaxy, combined. Some of that energy goes into making atoms beyond iron — nickel and lead, platinum and gold, uranium and thorium.

When air rises, it expands, and grows cooler. As air cools down, water vapor condenses, to form cloud droplets — like when you blow into a freezer.




Water sucks up heat when it evaporates (which is how sweat cools our skin). Water vapor condensing pulls the same trick backwards — when water vapor turns to liquid cloud droplets, the heat comes right back out. So when clouds form, they warm the air around them.

Warm air rises, of course, so the air around clouds rises yet more … expands … cools off … forms more clouds … and is re-warmed yet again … over and over, building towering thunderclouds miles into the sky.

When thunderstorms form off the coast of Africa, they feel the winds around them; they feel the spin of the Earth; they apparently feel other things we don’t know about yet.

Responding to their environment, clusters of thunderstorms may organize — feed into and off of each other — and become hurricanes.

Stars are atom factories — sunlight is a by-product of the sun making helium. Stars larger than the sun make heavier atoms — carbon and oxygen, for instance. But no star makes atoms heavier than iron — iron is the heaviest atom a star can make, and still shine.

When really large stars runs out of fuel, it explodes, briefly giving off as much energy as all the stars in its galaxy, combined. Some of that energy goes into making atoms beyond iron — nickel and lead, platinum and gold, uranium and thorium.

Uranium and thorium are too large to hold together; sooner or later, they break apart: they’re radioactive.

Exploding stars seed the galaxy with atoms that will go into the next generation of stars and planets. Radioactive uranium and thorium inject heat into the rocks hundreds, thousands of miles beneath our feet.

Warm air rises; so does warm rock (and for the same reason). Warm rock is plastic — it can flow, even though it’s solid.

A thousand or more miles beneath our feet, warm rock rises upward, almost to the surface.

Then the rock moves sideways … and then it sinks back down, into the depths. Moving streams of rock carry continents and ocean floors, like flotsam, across the surface of the Earth. The streams pull continents apart, smash them together.

Until a hundred-plus million years ago, there was no Atlantic for hurricanes to form in — not until South America was pulled away from Africa, opening the Atlantic between them.

The Atlantic is growing wider, as the continents are pulled apart. But around the Pacific, continents and ocean basins, pushed into each other, are — inch-by-inch — closing the Pacific.

As the floor of the Pacific collides with North America, with South America — and, most recently, with Mexico — great earthquakes result.

Al Stahler enjoys sharing nature with students of all ages. His science stories can be heard on radio station KVMR (89.5 FM), and he may be reached at stahler@kvmr.org


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