Renewed volcanism built the postcaldera volcanoes of the central platform, Merriam Cone, and Wizard Island. Following the climactic eruption, it took perhaps 250 years of rain and snow accumulation for the caldera to fill to its present-day lake level. The lake level is maintained by a balance between precipitation and evaporation plus seepage. By that time, the postcaldera volcanoes, nearly all of which are hidden beneath the surface of the lake, had finished their eruptions of andesite lava. Only a small rhyodacite dome was erupted later, about 5,000 years ago.
Studies show that hydrothermal activities are present at the lake floor.
Chemical analysis of the lake water and hydrothermal studies indicate that warm water enters the lake from the lake bottom. The water is heated by hot rock beneath the fractured caldera floor. Scientists are not certain whether any magma still remains underground but it is likely that Mount Mazama will erupt again someday. The following diagrams show the formation of Crater Lake during the climactic eruption of Mount Mazama. Plinian eruption deposits airfall pumice and ash, blown by winds to north and east.