Gravity Currents

Question 1

What is a gravity current?

Answer 1

A flow phenomenon induced when fluid of one density impinges on fluid of a different density, usually at a horizontal boundary.

Question 2

Describe the movement of a dense current

Answer 2

Flows along basal surface and experiences friction. Leads to a “no-slip” condition with a raised nose and some fluid being overrun.

Question 3

Describe the movement of a light current

Answer 3

The fluid flows at the free surface, experiencing no friction, leading to a “free-slip” boundary condition.
The nose at the surface forms a wedge.

Question 4

What is an intrusion?

Answer 4

A gravity current which propagates along the interface between a heavier and lighter fluid.

Question 5

Describe the movement of a particle-laden gravity current.

Answer 5

1. Current gains buoyancy due to erosion and entrainment of particles (accelerates).
2. Current forms a balance of erosion/sedimentation and has a constant Froude number and buoyancy flux.
3. Current deposits sediments and loses buoyancy causing it to decelerate.

Question 6

Difference between Viscous and Inertial gravity currents

Answer 6

Viscous: low Reynolds number. Buoyancy forces are balanced by viscosity.
Inertial: high Reynolds number. Buoyancy forces balanced by dynamic pressure.