:::I don't understand. The confusion likely came from the sentence" "Subsequent volcanism during this volcanic phase constructed a significant lava dome on its summit." I changed that sentence to "Subsequent volcanism during this volcanic phase constructed a significant lava dome." because the lava dome did not form on the summit. The next sentence "This acts like a volcanic plug and composes the lava spines that currently form pinnacles on its rugged summit." is quite clear. The lava dome acts like a volcanic plug and composes the lava spines that form the pinnacles on the mountain's summit.