During this period, four episodes of magmatic eruptive activity have been recently recognized. Italy is the largest producer of pumice because of its numerous eruptive volcanoes. North Sister's lava flows demonstrate similar compositions throughout the mountain's long eruptive history. Goat Rocks is a stratovolcano with a somewhat complicated eruptive history. This crater is the site of all Holocene eruptive activity. However the X-ray emission is due to stable coronal structures and not eruptive flaring activity. Mapping of Carmelo and Sherman craters, and interpretations of the eruptive history, continue, as well. It has been considered that they became trapped during transport in the eruptive plume. Radiometric dating has shown that eruptive activity lasted from about . Danger from normal, explosive eruptive activity is limited to within Cotopaxi National Park. Mount Shasta has an explosive, eruptive history. It has since alternated between eruptive and calm periods. The latest minor eruptive event occurred in August 1907. Through early 1990, at least twenty-one periods of eruptive activity had occurred. Within these wide-defining eruptive types are several subtypes.