Valcanoes


 * Aa Lava**

‍viscosity
Viscosity, a of the resistance of a fluid which is being deformed by either shear stress or extensional stress. In general terms it is the resistance of a liquid to flow, or its "thickness". Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. Thus, water is "thin", having a viscosity, while oil is "thick" having a viscosity. All real fluids (except superfluids) have some resistance to stress, but a fluid which has no resistance to shear stress is known as an fluid or inviscid fluid. For example, a high viscosity magma will create a volcano, because it cannot fast enough; low viscosity lava will create a shield volcano, which is large and wide. The of viscosity is known as rheology.


 * ‍volcanic ash**