Question
Which of the following are true about explosive eruption?
A. As the magma rises, pressure buildup decreases.
B. Pressure in the surrounding magma is greater than
in the gas bubbles.
C. Pressure inside the gas bubbles is greater than the
surrounding magma.
D. As the magma rises, pressure buildup increases.
Answer (1)
The given question is related to geology and volcanic eruption patterns which falls under the main topic Geography. An explosive eruption happens when the pressure of trapped gases in a viscous high-silica magma becomes too great. Key parts are:1. 'Pressure in the surrounding magma is greater than in the gas bubbles.'This statement is tricky and somewhat false because usually the pressure within gas bubbles is greater than its surrounding which gives rise to eruption. For explosive eruption, pressure outside cannot be greater.2. 'As the magma rises, pressure buildup decreases.'This is a true statement if relating to most eruption behaviours; when magma rises to the earth's crust due to less external pressure, trapped gas bubbles get a chance to expand due to decreased surrounding pressure, reducing the pressure buildup within the magma itself.3. 'As the magma rises, pressure buildup increases.'This statement is contradictory to general eruption process and hence false.4. 'Pressure inside the gas bubbles is greater than the surrounding magma.'This statement is technically correct as the greater pressure in gas bubbles gives the motive for the magma to rise and reach the surface(read earth's crust) causing eruptions including explosive ones.
