Lanín is the easternmost volcano of a north-west south-east oriented chain of three large stratovolcanoes, Villarrica being the westernmost one and Quetrupillán the one in the middle. This alignment is attributed to the existence of a fault beneath the volcanoes. In historical times, Lanín has been the least active of these volcanoes. Apart from Quetrupillán and Villarrica, there are a number of old eroded remains of stratovolcanoes in the alignment.