Volcanoes

In his very influential post on map generation, Martin O'Leary commented that one thing he'd like to see done was volcanoes. So I've added volcanoes.

There are lots of different kinds of volcanoes, but for our purposes we'll just distinguish between shield volcanoes - which are broad with shallow slopes (such as those on the islands of Hawaii) - and stratovolcanoes - which are tall with steep slopes (such as Vesuvius). Most volcanoes are stratovolcanoes.

We can also distinguish between volcanoes that occur at boundaries between tectonic plates - more specifically, where oceanic plates are pulling away from each other (e.g. the Mid-Atlantic Ridge), and where oceanic plates are subducting underneath continental plates (e.g. the Andes) - and hotspot volcanoes, which are much rarer and occur just about anywhere.

It's easy to add volcanoes in mountain ranges that are drawn along the edges of continents. They don't stand out, because they're part of mountain ranges, but they're there. Hotspot volcanoes take a little extra work. For one thing, hotspot volcanoes often have extinct volcanoes nearby, because of the movement of the tectonic plate over the hotspot beneath. So UW creates those too. There isn't any functional difference between an active volcano and an extinct one other than that if you click on the crater of an active volcano it will tell you it's a volcano.

Stratovolcanoes appear as isolated peaks, with perhaps a subsidiary peak or two with their own craters. Here's a line of them - the one to the southeast is active, while the others are extinct volcanoes formed by the same hotspot in earlier ages:

They look pretty small on the regional map, as you can see, but bear in mind that this map is at a scale of one pixel per kilometre. Compare the scale and general shape of Vesuvius, and I think these are about right:

Shield volcanoes, meanwhile, are done by raising the land round about to create a wide, gradual slope, surmounted by a relatively low peak with a system of nice buttresses around it. These are much rarer than stratovolcanoes but can be quite impressive features when they do appear:

And here is a chain of shield volcanoes. The one furthest to the east is the active one, and the others are extinct. I like how lakes have unexpectedly formed on the slopes of this volcanic range (the active crater is just to the east of that lake in the centre of the last volcano):

(I know it looks like that river is going over the flank of the volcano to the west - it isn't really, it's running through a canyon between the volcano and the hills just to the west.)

Submarine volcanoes are also important, and we create them in a similar way to stratovolcanoes on land, with solitary peaks rising from the seabed. Again, the ones around the oceanic ridges mostly blend into those ridges, but the ones in other areas are more noticeable, especially if they have chains of extinct seamounts associated with them. Hotspot volcanoes are more common in the oceans than on land - unsurprisingly as oceanic crust is thinner than continental - and they tend to clump in particular areas, so UW models that too. Sometimes these rise above sea level and create volcanic islands:

Here's a close-up shot of some islands I liked - the large island has a stratovolcano in the middle, with three active craters. The whole island is covered in tropical rainforest. Clearly a good place to bury some pirate gold.

And of course the import feature now lets you import volcano maps, so you can add them to your custom worlds. This means that Mount Doom and the Lonely Mountain can be added properly to Middle Earth, which is clearly a major step forward.

Gondor came out a bit nicer this time too!