Complex sentence: Other than some past glacial activity, the arid climate of the Altiplano region has kept erosion rates low, meaning that the volcanic edifice is well preserved; on the flip side, lack of erosion also means that relatively little of its internal structure is exposed.
Split into simpler sentences: Other than some past glacial activity, the arid climate of the Altiplano region has kept erosion rates low, meaning that the volcanic edifice is well preserved. On the other hand, lack of erosion also means that relatively little of its internal structure is exposed.