The British Parliament passed a law granting independence in July 1947. The law gave people only one month to decide which country they wanted to live in and to move there. As millions of people began to move, more violence broke out.
Calderas form when an enormous magma chamber under, what was probably a pretty ginormous volcano, empties and collapses, causing the land above it to collapse as well. An explosive caldera-forming eruption has never been witnessed first hand, but we know that they should pretty fearsome spectacles. Much smaller calderas atop effusive volcanoes (hawaiian style) have been observed. So, formation: maars form when a vent intersects groundwater and blasts out the overlying material.
Etna has the longest history of documented eruptions of any volcano. The first reported eruption was in 1,500 BC. Close up view of the effusive vent taken on June 4, 1998. Photo by Boris Behncke. June 4, 1998 eruption of the southwestern vent of Voragine. Photo by Boris Behncke.