Part 4 (12 pts) A. What causes some volcanic eruptions to be effusive and some e
ID: 290895 • Letter: P
Question
Part 4 (12 pts) A. What causes some volcanic eruptions to be effusive and some explosive? (2 pts) B. Which type of magmas (basic, intermediate or silicic) are most likely to be explosive, and why? (2 pts) C. What are the two most important processes for changing the composition of a magma from mafic to felsic? (2 pts) What evidence supports these processes as causing the evolution of magmas from mafic to felsic? (3 pts) D. What is AFC? (Ipts) What is meant by the term MASH and where do MASH processes occur? (2 pts) Part 5 (6 pts) What type of tectonic activity is generating volcanic activity in the area of Yellowstone Park? (1 pt) What type of tectonic activity is generating volcanic activity in Hawaii? (1 pt) Draw two histograms of the volumes of different rock types (basic, intermediate and silicic) in Hawaii and Yellowstone Park? (2 pts) Why do Yellowstone and Hawaii have different distribution of erupted rock types? (2 pts) Park? (u A. B. C. two histograms of the volgrenerating olcaic D.Explanation / Answer
ANSWER-
A) Volcanic eruptions are caused by magma released into the surface.the factors that defines whether eruption is effusive or explosive depends on the the amount of volatiles present in the magma.Volatiles are substances such as such as H2O and CO2 that forms gas at relatively low pressure and temperature.Usually felsic/silicate melts with high gas contents and high viscosity are explosive ,whereas effusive when viceversa is the case.
B) Silicic magma are mostly explosive because they can contain higher amunt of volatiles/gas materials.
C) Two most important processes are-
-Assimilation: when a basic magma passes through cooler rocks upward,it partially melts the rock.since silica present in the rock melts at first place due to low melting temperature,it leads to addition of silicic magma to basic magma making it more siliceous.
Example- assimilation carbonate country rock by parent magma of the Panzhihua Fe-Ti-V deposit (SW China).
Crystal fractionation- its a mechanism where the mafic minerals in terms of density settles back and crystallize when the parent magma makes it way through the rocks leading to silica enrichment in the magma.Bowens reaction series showshow rocks gets fractionated from the parent magma.
Example- formation of island arcs dacite magma.
D) AFC stands for Assimilation-Fractional crystallization.
MASH stands for Melting,Assimilation,Storage and Homogenization (process).
Primary subduction zones are the ones where MASH processes occur especially island arcs.
PART 5-
A) The volcanic activity in the yellowstone park area is due to the the rifting of the North American plate which led to the formation of thermal mantle plumes and generating volcanoes and its activity in the area.
B)the volcanic activity in the hawaii is due to the movement of the pacific tectonic plate over a mantle plume ,making Hawaii an important hotspot.
D) The reason for different distribution of erupted rock types are due to the different composition of magma that is expelled into the surface.hawaiin eruptions are usually gentle and effusive because the magma is basaltic with low volatiles such as water.yellowstone volcanoes are characterized by flow of rhyolitic magmas leading to explosive eruptions with calderas present everywhere.