FIGURE 6.7 Example of an erupting geyser in Yellowstone Na- FIGURE 6.6 Example of a freshwater spring.This photograph tional Park.These hot springs are commonly caused by collection of shows subterranean water bubbling forth and the photosynthetic rainwater under pressure in hot rocks below ground.The water populations associated with this type of environment.Primary pro- turns partly to steam and causes the water above it to overflow, ducers predominate in these environments,where there is typically thereby reducing the pressure and leading to an eruption.(From ittle organic carbon originating from the subsurface source.(From Corel Gallery www.corel.com) Corel Gallery www.corel.com)