What youíre looking at is a mud pool in Yellowstone National Park. I donít completely understand the chemistry of it, but it goes something like this. Hydrogen sulfide gas erupts from the volcano deep underground. When it reaches the surface, it combines with snow melt to create sulfuric acid. This acid breaks down the rock, releasing iron. The iron and sulfur combine to create iron sulfide which causes the black streaks on the water. As the gases erupt at the surface, it also creates waves. As the waves hit the land, rip currents are created. This causes the swirls on the water. Pretty cool stuff, I think.