This collision model drifts far enough from reality to cause significant problems. The plate with the lowest density eventually gobbles up all the other plates, while previously subducted cells do not fill with rock when at divergent boundaries, causing holes in the world like the one above.

My next project will be to replace convergent boundaries with an algorithm that takes into account full plate compositions. Divergence should be replaced such that each plate along a divergent boundary grows in a similar manner to what we see on Earth.

Supercontinent Cycle

To match the cycle seen on Earth, and to ensure that the model doesn’t stagnate, plates are split every 300–500 million years along a triple junction such that they split at an angle of 120 degrees. The lines along which plates split are currently linear, so some mountain ranges are a little too straight. Eventually I would like to add some random variance to this line.

Erosion

The erosion model I’m using has two components. The conversion from hard continental crust to sediment, and then sediment transport. Both need the addition of variable precipitation across cells, but still produce nicer elevation distributions than the simpler smoothing erosion I tried initially.

The creation of sediment currently depends on a cell’s slope to its downhill neighbors, as well as its elevation. Elevation dependence helps mitigate runaway mountain heights, but needs to be replaced with a more accurate glacial model once I have addressed the parts of the mountain problem caused by other pieces of the simulation.

Sediment movement uses an acyclic directed graph to transport sediment down in elevation. The amount of sediment removed from each cell is computed based on the average suspended sediment transported by major Earth rivers of differing slope. Sediment deposition could be improved as large piles currently end up on tiles at the bottom of the graph.

Initialization

The first initialization I used was a single circular landmass centered at a random point on the globe. While this single continent served well to see if collision and erosion were working, artifacts such as the one below dominated the landmass of each simulation run.

Triangular artifact from the starting circular continent.

Last week I implemented a meteor impact model to initialize the land, using a crater distribution from the late heavy bombardment period on Earth. Overlapping craters can be seen as they are currently additive in elevation, and ignore previous impacts. I will change this in the future. Without as direct of control on the crust distribution, mountains are back to taking over the world. However the the resulting landmasses appear much more natural in shape.