What is the main factor that determines whether a volcanic eruption is explosive or effusive? How does that factor affect eruptions in this way?


Viscosity is the main factor. Magma viscosity influences the explosiveness of a volcanic eruption through its effect on the dissolved gas content of the magma, which tries to escape the magma as the magma rises closer to the surface. Gases are not vented easily from more viscous magmas, allowing gas pressure to build.

Environmental & Atmospheric Sciences

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The fossil record reveals the true diversity of ancient plant and animal life

a. True b. False

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Organisms that are not attached to the bottom of the ocean are called ________ organisms.

Fill in the blank(s) with the appropriate word(s).

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What large city in Quebec, divided into Upper Town and Lower Town, is a cultural and tourist center because of its cultural landscape filled with narrow cobbled streets, small shops, and Parisian charm?

A) Montreal B) Quebec City C) Ottawa D) Gatineau

Environmental & Atmospheric Sciences