why does waves move towards the beach, and not “outwards” or “sidewards”?
In: Earth Science
The ocean is pulled a bit by the moon’s gravity. If there was no land, it’d just slosh around. We get ocean or lake waves when that sloshing is stopped by the land.
The waves are moving in different directions. The ones on the coast rise up because they are moving toward shallower water. The waves moving perpendicular to the coast are there, but not perceived because they and not moving toward the shore. At sea, you might not even know a large wave has passed because the waters are so deep that they don’t present on the surface.
Think of waves like giant ripples. You throw a pebble into a lake and the ripples start there and move outward,towards the shore. Now instead of a pebble in a lake the disturbances in the oceans are caused by storms, tectonic shifts and also moon gravity (tides).
Now you have giant ripples(waves). They don’t look like waves way out in the middle of the ocean, but once they get close to shore, the land drops off quickly and there’s sometimes rocks or reefs closer to shore, the sudden rise in the ocean floor will cause the waves to crest and break.
It is possible for these ripples (often called swells) to come to shore from directions that aren’t always perpendicular, though it’s often the case that even if they’re not straight-on it may appear close enough despite being slightly angled just because the scale is so large. With strong lateral currents and swells coming at off angles, it’s possible to see nearly sideways waves, but it’s not common, and will usually only show up in stormier conditions, likely with “regular” waves coming head on colliding with the ones coming at an angle.
Waves start in the middle of the ocean and move in every direction, mostly determined by the wind. When a wave gets closer to a coastline, the rising sea bottom makes the wave crest at the top.
If the shore was perfectly straight you’d see sideways waves, outwards would be unlikely as there is little force to create them there compared to what goes on in the middle of the ocean. But because the shore is almost never straight, each point tends to slow the waves and make them wrap around it, thereby making the waves more parallel to the shore
They almost never break perfectly perpendicular to the shoreline either, which is what surfers take advantage of to surf waves
You’ve got lots of good answers, but something I don’t see anywhere:
Waves move in all directions.
Most waves grow over large distances. They spend 1000 miles or more getting bigger and bigger. Because of those distances, waves that are big enough to really be seen when you’re standing on the beach must have come from somewhere 1000+ miles away. This means they come from out at sea.
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