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Theresa Kayzar “T.K.”

Lake “Rollover”
Investigating the Hazards of Lake Overturn

Stratified fluids that appear to be stable, meaning a heavier layer of fluid is located under an upper layer of less dense fluid, can be overturned if there is a heat flux into the system. In engineering literature, this type of overturn is called a “rollover” (Rice, 2000). In volcanic environments, rollover has been proposed to happen in volcanic lakes (Lake Nyos), and also in magma chambers.

Steps to Lake Overturn

1.

Heat flux

2.

Convection driven mixing

3.

Less density difference between layers

4.

Inversion of layers

(destabilization that leads to self mixing)

lake overturn

Hazard:
Gases stored at pressure in lower layers may exsolve eruptively

In the gas release of Lake Nyos, Cameroon, it is estimated that CO2 bubbles caused a jet as high as 80m to form and released gas that flowed into valleys at speeds of 72km/h (Holloway, 2000).

 The triggers of rollover are not as well understood as the process itself, and in volcanic environments there is much speculation.

 More specific to the volcanic lake setting, rollover is thought to occur when a gradual accumulation of CO2 through the lake bottom results in the saturation of the hypolimnion (The layer of water in a thermally stratified lake that lies below the thermocline). If heat is added to the hypolimnion, the water can be lifted and the total ambient pressure can decrease causing oversaturation and bubble formation. The exsolution of stored volatiles allows for an increase in buoyancy and turbulence within the fluid and breaks down the models of water column stability (Kanari, 1989; Kling, 1989).

Triggers for Rollover

Warming underlying layers

Injection of higher temperature fluid (volcanic or hot spring)

Cooling of upper layers

Rain (more dense upper waters)

Violent winds

Landslides

Earthquakes

(Holloway, 2000; Rice, 2000)

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