Landscapes Molten lava plateau Lava spreads out slowly Basic lava
Fissure eruptions Example: Antrim–Derry Plateau
Previous lava flows
Magma moves up through open fissure
Fig. 2.6(a) A fissure eruption.
A fissure eruption occurs when basic lava flows quietly from a linear crack in the earth’s crust (Fig. 2.6(a)). Fissures can be up to 50 metres in width, having been widened by the force of the rising magma. The lava spreads out slowly over a large area, often more than 50 km from the fissure (Fig. 2.6(b)). Repeated lava flows will result in the formation of a lava plateau.
Fig. 2.6(b) Basic lava flows from fissures.
Hydrothermal vents
Geysers Example: Old Faithful, Yellowstone National Park, Wyoming, USA
Geysers are springs which eject hot water with great force at frequent intervals. Water descends to the lower crust, where it is heated by the surrounding hot rock. Pressure builds as the water boils. Eventually a spray of hot water and steam explodes onto the earth’s surface.
Fig. 2.7 Old Faithful – Yellowstone National Park contains about half of the world’s geysers.
