The political events of the 1990âs have had significant effects on the number of Member. States of the United Nations. In 1990, the entry of both Namibia and Liechtenstein made the. number of members rise to 160; however the successive union of North and South Yemen, and.
Several types of volcanic eruptions âduring which lava, tephra (ash, lapilli, volcanic bombs and blocks), and assorted gases are expelled from a volcanic vent or fissure âhave been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed.here are two types of eruptions in terms of activity, explosive eruptions and effusive eruptions. Explosive eruptions are characterized by gas-driven explosions that propels magma and tephra. Effusive eruptions, meanwhile, are characterized by the outpouring of lava without significant explosive eruption.
Explosive Eruptions. A second category of volcanoes are those characterized by explosive eruptions. Explosive eruptions are common to volcanoes with very viscous lava and high amounts of gas under pressure.The viscosity, or stickiness, of the lava relates to the silica content.xplosive eruptions are common to volcanoes along the  Ring of Fire , a string of volcanoes extending from the northwest coast of the United States, up through the Aleutian Islands, and into Japan.