Is dizziness a symptom or a sign

Dizziness is a symptom. It can be a symptom of these causes:

Vertigo

Anxiety disorders

Low blood sugar (hypoglycemia). This condition generally occurs in people with diabetes who use insulin.

etc A feeling of being unbalanced or lightheaded.

the plates spread at mid-ocean ridges (they are divergent plate boundaries) which allows magma to rise through the weakness between the plates. the magma then emerges as lava from the boundary and cools, creating a new crust.