Tutorial: Creating a shield volcano with calderas

[su_liam]

While trying to help with wdmartin's Erobelis Isle thread, here, I discovered a pretty good way using only the Wilbur Mound tool to create a shield volcano studded with calderas much like Olympus Mons on Mars. A variant on this might prove useful in creating impact craters, but I'm not really going to deal with that here.

I'll start with a 1024x1024 blank map. To keep things sane, I'm just going to have this thing pop up out of a flat plane.

First, using the freehand selection tool with feather set to 1.0, select a roughly circular base for your volcano.


Because I want to give this shield a bit of a lip above the surrounding plains like the edge of Mons Olympus on Mars, I will set the minimum height to 300 meters. I arbitrarily choose a maximum height of 15000 meters, making this lower than Olympus Mons, but definitely more of a Martian volcano than Terrestrial. For a shield volcano on an earthlike planet 5 or 6 kilometers above sea level would be a really tall shield. Set the Operation to Add and Noise to zero.


Now click the Edit Profile button. Your goal here will be to create a fairly steep-sided flat-topped profile. I usually start by entering a value like 0.9 in the Non-Linearity and hit Apply several times till I like the shape. Next hand draw a flatter top to the curve, trying to keep it continuously rounded and monotonically increasing to the right. Repeated applications of Smooth, Non-Linearity and Normalize will help. With luck and a bit of work you'll end up with a curve similar to the one below. With more luck, experience and effort you could get better results. This is pretty quickly thrown together.


Next, we want to create a caldera. Select a large round area near the top of the previous mound. Invoke the Mound tool with the Minimum Height set to zero and the Maximum Height set to a negative value equal to the desired depth of your caldera. In this case, -3000. Most of the time you'll want a much steeper dropoff around the edge of the caldera than the edge of the shield. A few more applications of Non-Linearity, perhaps flattening off the top again, followed by more Smoothing and Normalize should do for that.