What features characterise a shield volcano compared to a composite volcano?

A shield volcano is characterised by its broad, flat shape, gentle slopes, and eruptions of low-viscosity lava.

Shield volcanoes are named for their distinctive shape, which resembles a warrior's shield lying on the ground. They are typically broad and flat, with gentle slopes that are the result of highly fluid, low-viscosity lava flowing out of the volcano during eruptions. This type of lava, known as basaltic lava, can travel great distances before cooling and solidifying, leading to the wide, expansive shape of shield volcanoes.

In contrast, composite volcanoes, also known as stratovolcanoes, are characterised by their steep, conical shape. This is due to the more viscous lava that they erupt, which cools and solidifies much more quickly, building up around the vent and creating a steeper slope. Composite volcanoes also often erupt explosively, throwing ash and pyroclastic material into the air, which can also contribute to their steeper shape.

Another key characteristic of shield volcanoes is their eruption style. Shield volcanoes typically have effusive eruptions, where lava flows out of the volcano steadily and relatively calmly. This is in contrast to the explosive eruptions often seen in composite volcanoes, which can be much more violent and destructive.

The location of shield volcanoes is also a distinguishing feature. They are most commonly found in oceanic settings, particularly in areas of the Earth's crust where tectonic plates are diverging or 'pulling apart'. This is because the magma that feeds shield volcanoes is typically produced by the partial melting of the Earth's mantle, which can occur more readily in these tectonic settings. The Hawaiian Islands, for example, are made up of shield volcanoes.

In summary, shield volcanoes are characterised by their broad, flat shape, gentle slopes, and eruptions of low-viscosity lava. They are typically found in oceanic settings and have effusive eruption styles. These features contrast with the steeper slopes, more viscous lava, and often explosive eruptions of composite volcanoes.