 A typical eruption along the Great Rift and similar basaltic rift systems starts with a curtain of very fluid lava shooting up to 1 @,@ 000 feet ( 300 m ) high along a segment of the rift up to 1 mile ( 1 @.@ 6 km ) long . As the eruption continues , pressure and heat decrease and the chemistry of the lava becomes slightly more silica rich . The curtain of lava responds by breaking apart into separate vents . Various types of volcanoes may form at these vents : gas @-@ rich pulverized lava creates cinder cones ( such as Inferno Cone – stop 4 ) , and pasty lava blobs form spatter cones ( such as Spatter Cones – stop 5 ) . Later stages of an eruption push lava streams out through the side or base of cinder cones , which usually ends the life of the cinder cone ( North Crater , Watchmen , and Sheep Trail Butte are notable exceptions ) . This will sometimes breach part of the cone and carry it away as large and craggy blocks of cinder ( as seen at North Crater Flow – stop 2 – and Devils Orchard – stop 3 ) . Solid crust forms over lava streams and lava tubes ( a type of cave ) , and are created when lava vacates its course ( examples can be seen at the Cave Area – stop 7 ) . 
