A geographer who studies how volcanic eruptions are shaping the Earth most often uses which of the six essential elements of geography?

physical systems

Explanation: The physical systems are one of the six essential elements of geography. These systems are the ones that are natural, and they shape the physical appearance of Earth because of its geological process. Part of these physical systems are the volcanoes with their eruptions. The Volcanoes are one of the major factors that influence the shaping of the Earth's surface, as they manage to propel enormous amounts of material from them, with the magma/lava being the one that usually covers the surface and creates new land forms. The volcanoes themselves create new forms, be it island chains or continental arcs.