This is a picture of a bomb. Fragments that are thrown up or ejected from a volcanic eruption are known as Volcanic Ejecta. Ejecta's are classified according to their size. Fragments larger than 1.5 inches in diameter are called bombs or blocks, depending on their shape. They are thrown out of an eruptions in a fluid state.
Bombs are blobs of lava, while blocks are jagged chunks of older rock.
As magma enters the zone of low pressure, gas starts to come out of solution and forms bubbles in the magma. This condition in which most magma erupts. Solidifying of rocks preserves the holes, which are known as vesicles. Extremely inflated, very light rock froth is pumice. Hawaiian pumice is called reticulite.