Fire and ice forged the terrain around Tower Fall in Yellowstone National Park. Today's devblog takes a look at that geologic history -- and how we're recreating that environment for the upcoming Tower Fall DLC map.
This area, which lies just north of the Yellowstone caldera, features an ancient volcano called Mount Washburn, which erupted around 640,000 years ago, spewing lava and ash. Some of the lava cooled quickly and formed blocky rocks called breccia. The upper slopes of the mountain are blanketed with dark, angular rocks. Creating this kind of landscape in the game has been difficult, since terrain textures can't render such sharp bumps without special techniques that have a major performance impact. But by using a Blanket shader (the same one that we're using for large grass patches), we can "wrap" rock meshes to the terrain, giving us good, realistic coverage which looks so much better than the plain terrain.
Many of these breccia rocks came to rest on the upper surfaces of the mountain, but others got caught in mudflows, which carried them farther downhill before cooling. As they cooled, those flows formed conglomerate rocks. These conglomerates along with the breccia form the slopes of Mount Washburn today.
During that eruption, Washburn also spewed out clouds of volcanic ash, which drifted away before settling onto the ground -- but the ash particles were still so hot, over 600 degrees celcius, that they welded together. This rock is now called welded ash or tuff, and that forms much of the northern areas of the game map. It's a hard rock indeed, but it has eroded in some places, such as the famous Devil's Den, just above the Tower Fall waterfall, where the creek has carved a crazy maze of spires and pinnacles.
Millions of years after these eruptions, the glaciers moved in, scouring the landscape and then as they receded, leaving behind a layer of glacial till. They also deposited many boulders (glacial erratics) and carved out a few glacial ponds. This left much of the game map a gentle landscape, with rolling hills and ravines in the Antelope Creek watershed, where the glaciers scoured the land and filled it in with gravel.
All this makes the Tower Fall map quite different from the granite landscapes of Slough Creek and Hellroaring. It's much more similar to Amethyst, with chunky, bumpy conglomerate rock formations and broad valleys and plateaus that are layered with glacial till. The only major topographical feature, besides Mount Washburn itself, is the Grand Canyon of the Yellowstone River, on the eastern edge of the map. The river has cut a deep canyon through various layers of conglomerate and glacial till -- but since it's mainly in this corner of the map, so you can just avoid that area if you want.
We have plenty more work to do on Tower Fall, including dens, so stay tuned for updates!