What characterizes hydrothermal metamorphism?

Hydrothermal metamorphism is characterized by the circulation of hot, ion-rich water. This process occurs when water, heated by nearby magma or geological activity, interacts with preexisting rocks. The elevated temperatures facilitate chemical reactions and the transportation of ions, which can lead to significant changes in the mineral composition and texture of the affected rocks. This process allows for the alteration of rock minerals and the formation of new minerals that may not have been present in the original rock, resulting in a metamorphosed rock with different physical and chemical properties.

The other options do not accurately define hydrothermal metamorphism. Heat from nearby lava flows can contribute to metamorphism but does not specifically characterize the hydrothermal process, which is defined by the presence of circulating water. Pressure from sediment accumulation is more associated with regional and contact metamorphism rather than hydrothermal metamorphism. Finally, exposure to extreme cold is unrelated to hydrothermal processes and does not drive metamorphism; rather, it can lead to other geological phenomena.