What is the difference between a ravine, gorge and canyon?
Solution 1:
Words aren't computer programs. They aren't exactly specified. There's a lot of room for slight differences. Pebble, stone, rock. Honesty, integrity, fidelity. Kingly, royal, regal.
There are no exact synonyms, but you can often replace one word for another and get by.
Definitions of words are not the words themselves. They are attempts at capturing how to use words, but you can't, as you can in math, replace a word with its definition and have everything work out as intended.
Lexicographers are highly knowledgeable about the nuances of words, but they are constrained by page space (or nowadays by reader attention) to limit the number of words in a definition.
Also, 'canyon' is a borrowing from Spanish into English and is common in the southwest US (like 'arroyo').
All that said, I share your vague perception that a canyon is bigger than a gorge which is bigger than a ravine (which is bigger than a gulley). I feel like a river goes through a canyon, a small river or stream through a gorge, a creek or brook through a ravine, and a gulley is often barely a stream to dry.
All that said, each of these words may have very specific technical definitions for use by geo-morphologists, possibly involving wall steepness/height/complexity (smooth vs jagged), volume of water, length, surrounding geology, etc. This may lead to things being called one thing in a gazette but called by scientists one of the others. (i.e. the Three Gorges on the Yangtze may be considered a canyon technically).
There are online glossaries or geomorphology. One gives
It gives for your desired terms the following:
Gorge A steep-sided, narrow floored valley cut into bedrock
Ravine - strangely, not defined but used multiple times for versions of ravine
Canyon A deeply incised, steep-sided river valley
Gully A small hollow or channel incised into sediments or unconsolidated rock by running water
For a very specified definition:
- Arroyo - Incised valley bottom, particularly in the western U.S. The arroyos can be cut as deeply as 20m, be over 50m wide and tens or even hundreds of kilometres long
There are all sorts of words for different scales and topologies of watershed areas: gulch, hollow, couloir, valley, coombe (or cwm for word-nerds) and on and on.
Note that these technical definitions are not as interreferenced as the informal definitions given by the dictionaries. I find the dictionary definitions you found to be somewhat unsatisfactory in comparison because of them each referring to the other.