lava

A lava fountain on Kilauea Iki, Hawaii, USA. As magma reaches the earth's surface escaping gas sprays lava into the air.

A lava bubble in Mauna Ulu, Hawaii, USA.

A knife-edge ridge of volcanic rock on the Napali coast of Kauai, one of the westernmost of the Hawaiian islands. Such a ridge may be formed when lava flows along a surface and drops into a crack or crevice, filling it up; the supporting sides eventually erode away, leaving only the shape of the original fissure.

From Hawaiian shield volcanoes, lava may flow smoothly and consistently for long distances. The smoothness of flow is partly due to the chemical composition of the lava which has a comparatively low proportion of silica (silicon dioxide) and a comparatively high proportion of calcium (as feldspar) and magnesium (as pyroxene).

A landscape of cooled lava, created by the 1973 eruption of the Helgafell volcano, on the Icelandic island of Heimaey. The eruption created a new peak, Eldfell, and a 3 km/1.9 mi lava flow, Eldfellshraun. Magma, rocks, ash, and soot were ejected. Since the eruption, the volcano has stabilized, and vegetation has begun to colonize the slopes.

Cooled lava and boulders in Heimaey, in the Western Islands (Vestmannaeyjar), Iceland. The volcano last erupted in 1973, ejecting magma, rocks, ash, and soot. The slopes have since stabilized, allowing plants to grow there once again. Moss and lichen can be seen on the rocks in the foreground.

Scree slope and cliffs near Eldborg, an ancient volcanic crater, in southern Iceland. Rocks fractured and broken apart by freeze-thaw action here form slopes of loose material. The slopes are very similar to the landscape of hot desert areas. Areas such as southern Iceland – which are called periglacial (literally on the edge of glacier activity) – are sometimes called cold deserts.

The slopes of Helgafell, a volcano on the island of Heimaey, Iceland. Helgafell last erupted in 1973. The eruption created the new Eldfell cone and a 3 km/1.9 mi lava flow. Although the lava slopes have stabilized, the soil remains very hot, and at a depth of 1 m/3.3 ft, the soil and rock hold temperatures up to 300°C/572°F. In the far distance another volcanic island can be seen.

Vegetation has now begun to recolonize the lava slopes of the Helgafell volcano, on the Icelandic island of Heimaey, which last erupted in 1973.

A slope of cooled lava, showing evidence of the 1973 eruption of the Helgafell volcano, on the island of Heimaey, in the Icelandic Westman Islands. Since the eruption, vegetation has begun to grow once more on the areas affected by the volcano, although temperatures just below the topsoil remain high.

A plain in southern Iceland covered with the remains of former lava flows. The Reykjanes peninsula has many lava flows, as well as geothermal fields and crater lakes. Tectonically active, Iceland is located on a mid-ocean ridge where the North American and European plates move apart.

Molten magma that erupts from a volcano and cools to form extrusive igneous rock. Lava types differ in composition, temperature, gas content, and viscosity (resistance to flow).

The three major lava types are basalt (dark, fluid, and relatively low silica content), rhyolite (light, viscous, high silica content), and andesite (an intermediate lava).

The viscosity of lava was once ascribed to whether it was acidic or basic. However, the terms acid rock and basic rock are misleading, and are no longer used as classifications.