Which of the following best explains how a tephra deposit forms?

a. highly fluid lava erupts from an active volcano and flows across great distances, slowly solidifying into a flat surface.
b. as magma is forced upward, it travels horizontally through cracks in the crust, solidifying into either long, horizontal shafts or saucer-shaped formations.
c. airborne ash and rocks from a volcanic eruption remain suspended in the air for a long time before eventually settling to the ground in a new location far from the volcano.
d. as magma is forced upward, it travels through vertical cracks in the crust, spreading outward and pushing up an overlying layer, creating a do

C. Airborne ash and rocks from a volcanic eruption remain suspended in the air for a long time before eventually settling to the ground in a new location far from the volcano.

Explanation:

Tephra deposits take many forms and shape, and their composition doesn't really matter either. The only thing that defines a tephra really is that it was ejected from the mouth of a volcano and fell on the ground where it remained intact (not merged with something else).

So, forms of tephra could be big boulders landing on the volcano's side or ashes that travel around the globe to land on the other side of the planet.

heat from the core of the earth causes convection currents to occur in the mantle. these currents slowly move the crust around.