Complex sentence: There are often whole areas or lines of pillow lava this is because when more magma rises from the mid-ocean ridge, the skin can no longer hold it in, so more pillow lavas erupt from the first one.
Split into simpler sentences: There are often whole areas or lines of pillow lava. This is because when more magma rises from the mid-ocean ridge, the skin can no longer hold it in, so more pillow lavas erupt from the first one.