This evolved into the second phase accompanied by broad regional metamorphism as thermal doming began. The proto-rift stage describes the rift onset with either doming or flexural subsidence. The area was also faulted by the doming action of the caldera before the eruption. This complex is characterized by a high doming with a central depression. Doming problems due to thermal expansion of the shadow mask was solved in several ways. The doming has resulted in the formation of a piedmonttreppen relief in southern Sweden. From deep within the Earth, hot mantle rises to force doming of the crust.