User:Ikluft/essay/Categorization of craters

Categorization of craters has been a source of recurring confusion over the years on Wikipedia. This essay presents lessons learned and best practices for creating and using categories about various kinds of craters. It also includes advice on what not to categorize as a crater.

The source of the confusion comes from the use of the word "crater" for several unrelated geological processes involving asteroid impacts, volcanic eruptions, or nuclear and chemical explosions. Over the years, many editors have looked at a topic and referred to it just as a "crater", leading to jumbled, disorganized categories containing articles and files with a mix of all kinds.

There are also some geological formations and map illusions which commonly are mistaken for craters. So this page will also point out items which should not be categorized as any kind of crater, and where to put them instead.

Background
In 2009, there were categories with names like "Craters", "Craters by country", "Craters of Canada", etc. Those categories had instruction that they were just for impact craters. But articles for other kinds of craters were continually being added to them by well-meaning editors who either didn't read or didn't understand the directions. Discussion led to a mass-renaming of 76 categories so those all had "impact craters" in their names, instead of just "craters". That worked well at resolving the confusion.

Lessons learned
Cleaning up the categories and answering questions has led to some advice: 1) don't just use "crater" without a type in a category name, and 2) re-created categories were marked as disambiguation or redirect to help editors find the right category.

Category name must include crater type
The big lesson learned from the 2009 mass renaming was categories about craters must include the type of crater in the name. They can be impact, volcanic or explosion craters, but not just craters. Otherwise it turns out to be too easy to find for editors to use tools like HotCat that only show the name of the category and none of the instructions on the category text.

Crater lakes have the same issues as craters, and should also be placed in qualified categories.

Craters category kept for disambiguation
Another lesson was learned 10 years after the renaming in 2019, after some of the original category names were re-created. Category:Craters started to fill up with a confusing mix of miscellaneous subcategories and articles again. After cleaning it out, instead of proposing to delete it, it was kept as a disambiguation category. It has specific instructions to use the specific category tree for the type of crater: Category:Impact craters, Category:Volcanic craters or Category:Explosion craters.

Also, Category:Craters on Earth was emptied and turned into a templated redirect to Category:Impact craters on Earth. If it had been deleted, it would eventually have been re-created too. So the redirect tells future editors the right place to go.

In November 2019, two CfR discussions sorted out crater lakes into Category:Volcanic crater lakes (see Crater_lakes CfR) and Category:Impact crater lakes (see Annular lakes CfR), leaving Category:Crater lakes as a disambiguation similar to Category:Craters.

Types of craters
So instead of just using the word "crater", now we know to specify which of several types of geological formations we mean:
 * Impact craters are the result of bolide (asteroid or comet) impacts on astronomical bodies, including Earth.
 * Categorize under Category:Impact craters
 * Volcanic craters resulting from volcanic eruptions include large calderas and small maars.
 * Categorize under Category:Volcanic craters
 * Explosion craters are formed by nuclear or chemical explosions on the ground or at shallow depth below the surface.
 * Categorize under Category:Explosion craters

Other formations, even if resembling craters, are considered depressions, not craters.

Impact craters
Impact craters are scientifically relatively new. Understanding of the geological structure and methods to prove or disprove an impact only began to be learned in the 1960s. This subfield of geology was originally established by Eugene Shoemaker when he found that Arizona's Meteor Crater had the same overturned structures and shocked minerals as Nevada's nuclear test craters, only much bigger. A detailed overview of the science of impact cratering is publicly available in the Lunar and Planetary Institute's e-book "Traces of Catastrophe", which is available for free download.

Impact crater lakes
Lakes in impact craters should be categorized under Category:Impact crater lakes.

Confirmed by citing Earth Impact Database
There is another common confusion when the news media reports a newly-discovered impact crater. Invariably, someone makes a good faith edit citing the news article and claiming the new crater is confirmed. But there is always more peer review to do at that point. So Wikipedia editors don't decide what is a confirmed impact - interpreting the evidence is just too easy to fall into a trap of original research.

The Earth Impact Database maintained by University of New Brunswick decides when an impact is confirmed. Confirmed impact sites have an EID entry. The parts of the URL can then be used in Wikipedia's Cite Earth Impact DB template to cite it as a reference. That automatically adds the article to Category:Earth Impact Database.

Possible impact craters
All other impact craters and structures, whether theorized or published in scientific journals and not (yet) listed in EID, go under Category:Possible impact craters on Earth.

However, there are lots of geological processes which can make circular or apparently circular features. Seeing a round feature on a map is not good enough to call something a crater, or even necessarily theorize about an asteroid impact. The rocks at the site have to be studied to seriously consider a new impact theory.

Impact craters on other astronomical bodies
Earth has many geological forces such as erosion and plate tectonics which cover and erase craters, renewing the surface. Contrast with the Moon where the surface geology is primarily driven by impacts. Depending on an astronomical body's amount of geological activity, there is little to no doubt whether a circular structure is an impact. So if astronomers and planetary scientists report via a reliable source a crater on another astronomical body, that's an acceptable source. Use the appropriate subcategory of Category:Impact craters on planets, Category:Impact craters on moons or Category:Impact craters on asteroids.

Volcanic craters
Volcanic craters should be categorized under Category:Volcanic craters or its subcategories. If reliable sources for geology call a structure a volcanic crater, caldera or maar, that's acceptable to call it and categorize it as a volcanic crater.

Types of volcanic craters
Some different eruption processes cause different types of volcanic craters, large and small.
 * A caldera is the largest volcanic crater, formed by a collapse of the volcano during an eruption.
 * Categorize under Category:Calderas
 * A maar is medium-sized compared to other volcanic craters, and is formed by an explosive eruption when magma comes in contact with groundwater. After the eruption ends, the maar may fill with water to form a lake.
 * Categorize under Category:Maars
 * Various volcanic cones may have a small crater where debris is deposited around an eruption vent at the summit or flank.
 * This doesn't currently have its own category. Use the appropriate subcategory of Category:Volcanoes.

Volcanic crater lakes
Lakes in volcanic craters should be categorized under Category:Volcanic crater lakes.

Explosion craters
Nuclear and chemical explosion craters should go in Category:Explosion craters or the appropriate subcategory.

There is no category for explosion crater lakes. For example, Lake Chagan is the only nuclear explosion crater lake. That isn't enough for a category according to WP:SMALL. (And let's hope there never are enough of those to make a category.) If there are lakes in other explosion craters, use Category:Artificial lakes.

Non-craters
There have been some cases of confusion by editors who wanted to call a sinkhole a type of crater. They aren't craters because they aren't the result of an explosion. They should go under Category:Sinkholes. Cave collapses are considered sinkholes, by definition.

Any other kind of depression which is not a crater should be categorized under Category:Depressions (geology).

Crater-related category discussions
The following Categories for Discussion items establish background and consensus around categorization of craters.