The rise and fall of the earth

We’ve all heard of ocean tides, but have you ever heard of land tides? Yes, just like the ocean, the earth’s crust rises and falls daily.


What do you want to know

  • The earth rises and falls like our ocean
  • The Sun and the Moon cause these earth tides
  • Earth’s tides could affect volcanic and seismic activity

What causes Earth’s tides?

Just like ocean tides, land tides occur due to the gravitational pull of the Moon and Sun.

We spoke to Dr. Andy Bobyarchick, a geologist in the Department of Geography and Earth Sciences and the University of North Carolina at Charlotte to find out more.

“The Moon’s position gravitationally creates a lunar tidal force that pulls the portion of the Earth facing the Moon, creating a slight outward bulge. This “high tide” occurs once per lunar day at a location specific geographic location. The Moon is where a low low would occur,” says Bobyarchick.

But how far does the Earth go up and down?

Bobyarchick states, “The Moon elastically deforms the whole planet, not just the surface. And depending on a number of factors, the displacement of the Earth’s surface by Earth’s tides can be a few tens of centimeters.”

So, of course, these earth tides are impossible to observe with the naked eye, but these small movements can cause impacts all over the world.

A gravimeter. (Dr. Andy Bobyarchick)

How Scientists Measure Earth’s Tides

Geologists use gravimeters to measure Earth’s tides.

According to Bobyarchick, “The simplest design for a gravimeter is a heavy mass suspended from a spring. The spring expands differently due to variations in the attraction of the mass.

“Drop towers where a mass is dropped a certain distance and the travel time of the mass to fall can also determine the local value of gravity. To measure tides, the gravimeter must be very sensitive.”

Why do scientists study Earth’s tides?

Studying Earth’s tides is useful when monitoring active volcanoes and seismic activity.

Bobyarchick says, “In terms of volcanic activity, Earth’s tides, by causing the crust to warp, also create stresses (pressure) in rocks. The movement of magma beneath a volcano means that molten rocks follow or create fractures, and tidal stresses could help this process.

“Similarly, earthquakes occur when rocks slide over fractures or when new fractures form, and tidal stresses can facilitate these processes. These causes and effects do not always apply to volcanic activity. or seismic, but some studies suggest that it is.”

There has been a correlation between Earth’s tides and volcanic eruptions, even though the stress on the planet created by Earth’s tides is extremely low. Earth tides could induce a faster eruption once gases and magma build up in the volcano before an eruption.

Scientists are still studying the connection between earth tides and earthquakes.

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