Complex sentence: Rootless cones can also be formed in lava flows when lava flows over wet sediments and vapor explosions open up the more less solid crust of the lava flow allowing spatter, tuff or cinder to be ejected.
Split into simpler sentences: Rootless cones can also be formed in lava when it flows over wet sediments. Vapor explosions then open up the crust of the lava flow allowing spatter, tuff or cinder to be ejected.