What Are Tides and What Causes Them?

What are tides? They are the rhythmic rise and fall of sea levels, orchestrated by celestial forces and Earth’s own movements.

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But their story is far richer than a simple gravitational pull—it’s a dynamic interplay of physics, geography, and even human civilization.

For centuries, sailors, fishermen, and coastal communities have relied on tidal patterns for survival. Today, scientists study them to predict climate change impacts and harness renewable energy.

Yet, despite their familiarity, tides remain one of nature’s most misunderstood phenomena.

How exactly does the Moon’s gravity drag entire oceans across the planet? Why do some coasts experience dramatic tidal swings while others barely notice the change?

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And what happens when storms, climate shifts, and human engineering interfere? Let’s dive deeper.

The Cosmic Ballet: Moon, Sun, and Earth’s Tug-of-War

Gravity is the unseen hand shaping tides. The Moon, though smaller than Earth, exerts a staggering influence. Its gravitational pull stretches the ocean, creating bulges—high tides.

But it’s not just the Moon’s tug that matters—it’s also Earth’s response. As our planet rotates, different regions pass through these bulges, resulting in the familiar high-low tide cycle.

The Sun plays a supporting role. Though 390 times farther away than the Moon, its massive size means it still affects tides.

When the Sun and Moon align (during new and full moons), their combined gravity creates spring tides—higher highs and lower lows.

When they’re at right angles (quarter moons), their forces partially cancel out, leading to milder neap tides.

Why doesn’t the Moon simply pull all the water away? Earth’s rotation and inertia keep the oceans in check, creating a delicate equilibrium.

Without this balance, coastlines would face catastrophic flooding every day.

Interestingly, tides aren’t instantaneous. Water has inertia, meaning it takes time to respond to gravitational shifts.

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This lag explains why high tide doesn’t always coincide exactly with the Moon’s zenith.

Beyond Gravity: The Overlooked Forces Shaping Tides

While the Moon and Sun dominate the conversation, other factors sculpt tidal behavior. Ocean basins, coastal shapes, and even weather systems alter how tides manifest.

Take the Bay of Fundy in Canada, home to the world’s most extreme tides. Its funnel-like shape amplifies tidal surges, creating a staggering 16-meter (52-foot) difference between high and low tide.

Meanwhile, the Mediterranean Sea, nearly landlocked, sees tides of just a few centimeters.

Winds and storms can override astronomical tides. Hurricane Katrina’s storm surge reached 8.5 meters (28 feet), drowning New Orleans in a way no normal tide ever could.

Similarly, seasonal monsoon winds in the Indian Ocean push water far beyond predicted tidal ranges.

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Even Earth’s rotation plays a role. The Coriolis effect—the same force that twists hurricanes—deflects tidal currents, creating complex circulation patterns.

In some places, like the English Channel, tides behave more like a sloshing bathtub than a simple rise and fall.

A Statistic That Anchors the Theory

NASA’s satellite data confirms: the Moon’s pull doesn’t just move water—it slows Earth itself.

Over centuries, tidal friction has increased the length of a day by 1.4 milliseconds per century. In other words, tides are stealing Earth’s rotational energy, gradually stretching time.

Tides and Human Civilization: A Complicated Relationship

Coastal cities have always lived at the mercy of tides. Venice’s acqua alta floods, worsened by sinking land and rising seas, now submerge the city multiple times a year.

Meanwhile, the Netherlands has spent centuries battling tides with dikes and storm surge barriers.

But tides aren’t just a threat—they’re also an opportunity.

Scotland’s MeyGen tidal energy project generates enough electricity to power 2,000 homes, proving that tides can be a reliable renewable resource. Similar projects are underway in South Korea and Canada.

Yet, human interference can backfire. Dams and coastal development disrupt natural tidal flows, sometimes leading to unexpected erosion or sediment buildup.

The shrinking of Louisiana’s wetlands, partly due to levees blocking tidal nourishment, shows how fragile these systems are.

An Analogy to Simplify the Science

Imagine Earth’s oceans as a cup of coffee. The Moon’s gravity tilts the cup, making the liquid slosh toward one side (high tide).

Now spin the cup (Earth’s rotation), and the coffee keeps sloshing in a rhythmic pattern. Add a second hand (the Sun) occasionally tilting the cup further or stabilizing it, and you’ve got the full tidal dance.

The Future of Tides in a Changing Climate

Rising sea levels are amplifying tidal impacts. NOAA predicts that by 2050, high-tide flooding in U.S. coastal cities could occur 10 times more often than today.

Places like Miami and Bangkok already face routine “sunny day flooding” during king tides.

Meanwhile, melting ice caps could alter ocean currents, potentially shifting tidal patterns in unpredictable ways. Some studies suggest the Bay of Fundy’s tides might grow even more extreme as sea levels rise.

The question isn’t just how tides will change—but how humanity will adapt. Will we build higher seawalls, retreat inland, or find ways to work with the tides instead of against them?

Conclusion: More Than Just Water Moving

What are tides? They are a symphony of physics, geography, and time. They shape ecosystems, influence cultures, and even hold the key to sustainable energy.

Yet, as climate change accelerates, the rules of this ancient dance are shifting. Understanding tides isn’t just about science—it’s about preparing for a future where the ocean’s rhythm grows more unpredictable.

Frequently Asked Questions

1. Why are there two high tides a day?

Most places experience two high tides because Earth rotates through two tidal bulges (one facing the Moon, one opposite).

2. Can tides affect the weather?

Indirectly—tides influence ocean currents, which then impact climate systems like El Niño.

3. Do lakes have tides?

Yes, but they’re extremely small (a few centimeters) because lakes lack the vast volume needed for noticeable gravitational pull.

4. How do tides impact marine life?

Many species, like crabs and mollusks, rely on tidal cycles for feeding and reproduction.

5. Could we ever control tides?

Not on a large scale—the forces involved are too massive. But we can harness tidal energy and mitigate flooding.

Enrique 13 de May de 2025

Oceanography