during a single eruptive phase that lasts a few days to a few years.Other volcanic landforms are not volcanoes at all.For example,Alaska's Valley of ten Thousand Smokes is a flat-topped deposit consisting of 15 cubic kilometers of ash that erupted in less than 60 hours and blanketed a section of river valley to a depth of 200 meters (600 feet). Volcanic landforms come in a wide variety of shapes and sizes, and each structure has a unique eruptive history. Newertheless,vol-canologisth have been able to classify volcanic landforms and determine their eruptive pat terns. In this section we consider the general anatomy of a volcano and look at three major volcanic types: shield volcanoes, cinder cones, and composite cones. Anatomy of a Volcano
Volcanic activity frequently begins when a fis-sure (crack) develops in the crust as magma moves forcefully toward the surface. As the gas-rich magma moves up through a fissure,itspatl is usually localized into a circular