Ethiopian volcano Erta' Ale' (Pronounced "Er-tah-All-Ey") is classified as constantly active, but it seldom produces very powerful eruptions.
Most of its observed life (since 1960), it has consisted of a "static lava lake" with small eruptions (only 2 on a scale of 10) like the one in this video:
Erta' Ale' is over an area where the earth's crust is diverging and the mantle (the very hot layer below the crust) is directly exposed at the surface. The theory about its lack of eruptive power is because the magma/lava is so close to the surface that it doesn't have a chance to pick up "volatiles" (such as water which generates superheated steam) needed to create more powerful eruptions.
The analogy is often made that Erta' Ale' is like a muscle car with only a teaspoon of gas in the tank.
Most of its observed life (since 1960), it has consisted of a "static lava lake" with small eruptions (only 2 on a scale of 10) like the one in this video:
Erta' Ale' is over an area where the earth's crust is diverging and the mantle (the very hot layer below the crust) is directly exposed at the surface. The theory about its lack of eruptive power is because the magma/lava is so close to the surface that it doesn't have a chance to pick up "volatiles" (such as water which generates superheated steam) needed to create more powerful eruptions.
The analogy is often made that Erta' Ale' is like a muscle car with only a teaspoon of gas in the tank.