Complex sentence: At present, there is some concern about the state of "dormancy" of Marsili, which is 3,000 meters high with the cone reaching to 500 meters from the surface of the water.
Split into simpler sentences: At present, there is some concern about the state of "dormancy" of Marsili. It is 3,000 meters high with the cone reaching to 500 meters from the surface of the water.