Complex sentence: The northernmost volcanoes are the highest, lie on thicker crust which causes their magmas to have a stronger crustal contribution, are dominated by andesitic and more evolved magmas and have the highest quantity of incompatible elements in their magmas.
Split into simpler sentences: The northernmost volcanoes are the highest and lie on thicker crust which causes their magmas to have a stronger crustal contribution. The output of the northernmost volcanoes is dominated by andesitic and more evolved magmas and they have the highest quantity of incompatible elements in their magmas.