Complex sentence: In the computer simulations, mounds naturally emerged from the landscape, and reached topographic maturity after hundreds of year of gopher activity, which could explain why nobody has ever witnessed the growth of one.
Split into simpler sentences: In the computer simulations, mounds naturally emerged from the landscape. In addition, the model showed that mounds reach topographic maturity after hundreds of year of gopher activity, a good explanation for why nobody has ever witnessed the growth of one.