What Happens if the Moon Crashes into Earth?
Why Worldbuilding Stack Exchange recommends it
Worldbuilding Stack Exchange users link it as a reference for how extreme tides, tsunamis and a ring system would behave when a moon gets very close to its planet.
Recommended by 2 people across 2 different months, 2018 to 2024.
What it is
A Kurzgesagt animated explainer that walks through what would happen if the Moon were pulled toward Earth, covering tidal forces, huge ocean waves, crustal stress and the possibility of the Moon breaking into a ring. It is narrated by Steve Taylor and includes a sources page for the science.
What people said
Recommends The Square-Cube Law · 2018-03 · Worldbuilding Stack Exchange · on “Reality Check - Collision of a Moon prevented by turning it into a ring”
Edit: it's been six years or so since I answered the question. To honor the votes I got so far I will leave my original answer below, I just want to say that I think a bit differently now. A ring around the Earth and anything that could even make it would be the cause of a global level extinction, but the rings might be stable for maybe millions of years and life could "restart" (geologically) quick after the rings formation, so the scenario in this question seems feasible. This video about the Moon nearly colliding with the Earth, but becoming a ring system instead [this video] is great food for thought. It's from my favourite popular science channel. I am writing a story with similar premises,
Recommends subrunner · 2024-04 · Worldbuilding Stack Exchange · on “Roughly how big could the tidal range be on a human habitable Earth analogue world?”
Have a look at this: [this video] It kinda shows how big the tides get before the earth crust gets moved so far that constant earth quakes and volcanic eruptions make life impossible.
Cites Kazon · 2023-07 · Worldbuilding Stack Exchange · on “Orbital limit for a sapient-habitable moon?”
How far does a moon need to be from the roche limit for sapient life to evolve? This is something I've been wondering about for ages. Life on exomoons seems to be a really unexplored subject in science, despite having quite a presence in fiction. I only know that at a distance of about 10 parent radii, the odds of a runaway greenhouse effect due to proximity to the host are reduced significantly [LINK] . I know this is probably very unorthodox, but out of desparation, I looked to Kurzgesagt's video on what would happen if Luna crashed into Earth [this video] . Using an equally unorthodox method (messing around in Universe Sandbox), I got an upper tidal-force limit of either 1.54E+21 or 2.53E+21 N
Cites The Square-Cube Law · 2024-07 · Worldbuilding Stack Exchange · on “Three kilometers (~2 miles high) tsunamis go around the Earth - what kinds of ruins are left?”
I am (still) writing some fiction about the solar system being rearranged, with the Earth losing the Moon. But before she goes, I am having her do a close flyby. My story is actually happening millennia after the fact. I am trying to come up with some worldbuilding that realistically reflects the destruction caused by such an event, and how much descendants of the survivors of the cataclysm can recover and parse from the past via whatever ruins are left. I have seen this video from Kurzgesagt [this video] where they say that should the Moon come very close to Earth, the tides would pull the oceans into 3km high waves (about 2 miles high, in imperial measure) going around the globe. There would al