How Buoyant Magma Erupts on the Surface( 1) a Magma is less dense than the solid rock from which it forms The pressure is proportional to depth (thickness of overlying rock). Therefore, as magma rises upward, the pressure on it decreases
How Buoyant Magma Erupts on the Surface (1) ◼ Magma is less dense than the solid rock from which it forms. ◼ The pressure is proportional to depth (thickness of overlying rock). ◼ Therefore, as magma rises upward, the pressure on it decreases
How Buoyant Magma Erupts on the Surface(2) Pressure controls the amount of gas a magma can dissolve--more at high pressure, less at low Gas dissolved in an upward-moving magma comes out of solution and forms bubbles
How Buoyant Magma Erupts on the Surface (2) ◼ Pressure controls the amount of gas a magma can dissolve—more at high pressure, less at low. ◼ Gas dissolved in an upward-moving magma comes out of solution and forms bubbles
Eruption Style--Nonexplosive or Explosive? (1) Nonexplosive eruptions occur notably in Hawaii, Iceland, and the seafloor. They are relatively safe a The difference between nonexplosive and explosive eruptions depends largely on magma viscosity and dissolved-gas content. a low viscosity magmas and low dissolved gas contents produce nonexplosive eruptions
Eruption Style—Nonexplosive or Explosive? (1) ◼ Nonexplosive eruptions occur notably in Hawaii, Iceland, and the seafloor. ◼ They are relatively safe. ◼ The difference between nonexplosive and explosive eruptions depends largely on magma viscosity and dissolved-gas content. ◼ Low viscosity magmas and low dissolved gas contents produce nonexplosive eruptions
Eruption Style--Nonexplosive or Explosive?(2) a Nonexplosive eruptions may appear violent during their initial stages The reason is that gas bubbles in a low. viscosity basaltic magma will rise rapidly upward, like the gas bubbles in a glass of soda a If a basaltic magma rises rapidly, spectacular lava fountains will occur
Eruption Style—Nonexplosive or Explosive? (2) ◼ Nonexplosive eruptions may appear violent during their initial stages. ◼ The reason is that gas bubbles in a lowviscosity basaltic magma will rise rapidly upward, like the gas bubbles in a glass of soda. ◼ If a basaltic magma rises rapidly, spectacular lava fountains will occur
Eruption Style--Nonexplosive or Explosive?(3) Because heat is lost quickly at the surface of the flowing lava, the surface solidifies into a crust, beneath which the liquid lava continues to flow in well-defined channels called lava tubes The very fluid lava initially forms thin pahoehoe flows With increasing viscosity the rate of movement slows and the stickier lava may be transformed into a rough surfaced aa flow that moves very SOW
Eruption Style—Nonexplosive or Explosive? (3) ◼ Because heat is lost quickly at the surface of the flowing lava, the surface solidifies into a crust, beneath which the liquid lava continues to flow in well-defined channels called lava tubes. ◼ The very fluid lava initially forms thin pahoehoe flows. ◼ With increasing viscosity the rate of movement slows and the stickier lava may be transformed into a rough surfaced aa flow that moves very slowly