Phreatomagmatic eruption

Phreatomagmatic eruptions are defined as juvenile forming eruptions as a result of interaction between water and magma. They are different from magmatic and phreatic eruptions. The products of phreatomagmatic eruptions contain juvenile clasts, unlike phreatic eruptions, and are the result of interaction between magma and water, unlike magmatic eruptions. It is very common for a large explosive eruption to have magmatic and phreatomagmatic components.

Mechanisms

Several competing theories exist as to the exact mechanism of ash formation. The most common is the theory of explosive thermal contraction of particles under rapid cooling from contact with water. In many cases the water is supplied by the sea, for example with Surtsey. In other cases the water may be present in a lake or caldera-lake, for example Santorini, where the phreatomagmatic component of the Minoan eruption was a result of both a lake and later the sea. There have also been examples of interaction between magma and water in an aquifer. Many of the cinder cones on Tenerife are believed to be phreatomagmatic because of these circumstances.

CBS Evening News

The CBS Evening News is the flagship evening television news program of CBS News, the news division of the CBS television network in the United States. The program has been broadcast since 1948 under the original title CBS Television News, eventually adopting its current title in 1963. Since June 6, 2011, the weekday editions of the program have been anchored by Scott Pelley. Since 2012, Jim Axelrod has served as anchor of the Saturday edition, while Jeff Glor anchors the Sunday edition. Previous anchors have included Douglas Edwards, Walter Cronkite, Dan Rather, Bob Schieffer, and Katie Couric.

The program's Monday through Friday editions air live at 6:30 PM in the Eastern and 5:30 PM in the Central Time Zones, and are tape delayed for the Mountain Time Zone. A separate "Western Edition", featuring updated segments to provide coverage of breaking news stories, airs live at 6:30 p.m. in the Pacific Time Zone and on tape delay in the Alaska and Hawaii–Aleutian Time Zones.

Anchors

Evening News

Evening News may refer to:

Television news

Newspapers

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Types of volcanic eruptions

Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series.

There are three different types of eruptions. The most well-observed are magmatic eruptions, which involve the decompression of gas within magma that propels it forward. Phreatomagmatic eruptions are another type of volcanic eruption, driven by the compression of gas within magma, the direct opposite of the process powering magmatic activity. The third eruptive type is the phreatic eruption, which is driven by the superheating of steam via contact with magma; these eruptive types often exhibit no magmatic release, instead causing the granulation of existing rock.