In continental areas associated with a mantle hot spot there may be eruption of large amounts of lava and pyroclastic material from multiple vents and fissures forming a flood basalt province. Valleys become filled and pre-existing landforms completely envel- oped when flood basalts cover many thousands of square kilometres, with successions that can be sev- eral thousand metres thick. Where individual vents build up a volcano by the repeated eruption of basaltic magmas they tend to have relatively gentle slopes and are known as shield volcanoes. Associated eruptions of basaltic pyroclastic material form scoria cones, circular landforms that may be only a few hundred metres across but with steep sides. Other morphologi- cal types of crater composed of volcaniclastic material are maars, which have steep-sided craters and gentle outer slopes, tuff rings that have roughly equal slopes either side of the rim and tuff cones that have steep outer cones and small craters. These all have relatively low preservation potential because they are composed of loose material and are hence readily reworked. Weathering processes acting on basaltic material rapidly lead to breakdown and theformation of pedogenic profiles (9.7) that may be recognised, often as reddened units within the succes- sion. Deposition of volcanic material over wide areas affects the fluvial systems and rivers tend to incise to form valleys within the succession. The fluvial depos- its within these valleys can be preserved by overlying volcanic units.