Caves, Quakes, and Underground Wonders

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Earthquakes and Caves—What’s Going On Underground?

Earth's Surface Is Always Changing

The earth may look still, but it’s actually in constant motion. Deep underground, there are forces shaping the surface—some slowly and quietly, others with a big jolt.

These forces form caves, mountains, earthquakes, and more. They are part of the earth’s internal energy, and they work around the clock.

What Causes Earthquakes?

The earth’s crust is made of massive puzzle pieces called tectonic plates. These plates float on top of the hot, soft mantle beneath them.

As they move, they sometimes bump into each other, pull apart, or slide past one another. When they do, stress builds up—until it releases suddenly in a shake called an earthquake.

That shaking can be small and barely noticeable, or strong enough to knock down buildings.

Here are key terms to remember.

Fault: A crack in the earth's crust where plates slip.

Epicenter: The spot on the surface right above where the earthquake starts.

Hypocenter: The exact point underground where the quake begins.

Seismograph: A machine scientists use to measure how strong the earthquake is.

Magnitude: The amount of energy released.

There are three main ways plates move.

Convergent – Plates collide. One slides beneath the other, causing powerful quakes.

Divergent – Plates move apart. These often form new ocean floors.

Transform – Plates slide sideways past each other. This can cause a lot of shaking.

Sometimes earthquakes happen deep under the ocean. If the sea floor shifts, it can push water into a giant wave called a tsunami.

What Are Caves?

Caves are hollow spaces in the ground that form naturally. Some are formed by lava or ice, but many of the world’s most famous caves are made by water.

Over time, rainwater seeps into the ground. As it travels through rock, especially limestone, it picks up tiny bits of minerals and slowly wears the rock away.

This creates open spaces underground, and those spaces are caves.

One amazing feature of many caves is the stalactites and stalagmites that form inside.

Stalactites hang from the ceiling.

Stalagmites rise from the ground.

They form when water carrying dissolved minerals drips from the cave roof. As the water drips and dries, it leaves behind tiny deposits of rock.

Over many, many years, these deposits build up into icicle-like shapes.

Here is a fun way to remember them.

Stalactites hold “tight” to the ceiling (or have a “C” for ceiling).

Stalagmites “might” reach the ceiling from the ground (or have a “G” for ground).

These formations grow extremely slowly—some only grow about a quarter inch every hundred years.

But over time, they become beautiful and massive.

What Do Earthquakes and Caves Have in Common?

Both are caused by water, heat, and pressure deep in the earth. Caves form slowly and quietly, shaping the underground world. Earthquakes strike suddenly and loudly, shaking the ground above.

Even though they’re different, both remind us that the earth is always active—even when it looks peaceful on the surface.

Test What You Know...

Now that you've uncovered what causes earthquakes and how caves take shape drop by drop, it's time to put your learning into action.

Head to the Got It? section and shake up some review.