QUESTION 8 Chapter 3.2.1. True/False: Magmas like rhyolite with high Sio2content

Question

QUESTION 8 Chapter 3.2.1. True/False: Magmas like rhyolite with high Sio2content tend to have a high viscosity (resistance to flow), while magmas like basalt with low SiO2content tend to have a low viscosity and flow very easily. O True False QUESTION 9 Chapter 3.2.1.Box 3.2. What is a continental flood basalt province? e a When a lava flow causes a river to be dammed, resulting in a flood. Ob-A massive lava flow at mid-ocean ridges that produces new oceanic crust. c, when basalt lava flows cover very large areas of continental crust. O d. A very low viscosity lava flow that fills an impact crater QUESTION 10 Chapter 3.2.2. Which combination of viscosity and gas content of the magma is most likely to lead to a very explosive volcanic eruption? O a low viscosity, low gas content O D low viscosity, high gas content c, high viscosity, low gas content o d high viscosity, high gas content

Explanation / Answer

1) True,

High SiO2 content Magma tends to be highly viscous   because of partial melting of country rock. Highly viscous Magma can trapped high amount of gas. Mostly H2O is present as a volatile in the felsic ro highly viscous Magma like Rhyolite.

Basaltic Magma contain low SiO2. This leads to low viscous Magma((Highly mobile). And hence can't trap volatile.

2) when basalt lava flows Cover very large areas of continental crust.

Mantle plume is the major source for flood basalt. Columbia River basalt, Deccan trap in India are some example of Continental flood basalt.

Mantle plume continously supply the Magma to the surface.

3) High viscous, high gas content

The rhyolitic or andesitic Magma are highly viscous and high gas content Magma. The viscosity and volatile content determines how explosive will be the eruption.

The Magma which partially melts the country rock will contain high SiO2. The SiO2 forms strong bonds in the Magma and forms the crystal in Magma which leads to make Magma more viscous. The more viscous Magma will trap the volatiles ( mostly H2O). When Magma comes to the surface, the gas cannot release easily and hence forms the bubble. This bubble try to escape to atmosphere and hence make it explosive eruption.

Explosive eruption gives more pyroclastic material like pumice, ash, scoria etc.

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