the source of conspicuous black lava flows in the western part of the field; some lava flows are over long. Los Morados is a complex of scoria cones and vents of different ages which during its emplacement underwent a sector collapse, intense Strombolian activity and a lava flow-induced rafting and re-healing of its slopes. On the southeast and east Los Morados is bordered by a lapilli plain, the Pampas Negras, which was formed by fallout of Strombolian eruptions and is being reworked by wind with the formation of dunes. Morado Sur consists of two aligned cones that formed in the same eruption and are covered with reddish deposits; it also features several vents and lava flows. Volcán Santa María is a cone with a small crater and also covered with red scoria and lava bombs. It is high and is associated with an area called "El Sandial", where lava bombs have left traces such as impact craters and aerodynamically deformed rocks. Pampas Onduladas and other giant lava flows Payún Matrú is the source of the longest Quaternary (last 2.58 million years ago) lava flow on Earth, the Pampas Onduladas lava flow in the eastern and northern sector of the volcanic field. The flow originates on the eastern side of the volcanic field in the La Carbonilla fault and eventually splits up into a shorter ("Llancanelo lava flow", long) northwestern and the longer southeastern branch which reaches all the way to an alluvial terrace of the Salado River in the La Pampa Province. This compound lava flow moved over a gentle terrain and is covered by lava rises and lava tumuli especially in areas where the flow encountered obstacles in the topography. There is some variation in its appearance between a wide, leveled initial proximal sector and a more sinuous distal sector. The unusually fast flowing lava under the influence of its low viscosity and of a favourable topography eventually accumulated to a volume of at least , a surface area of about and depending on the measurement a length of . The process by which such long lava flows form has been explained as "inflation" whereby lava forms a crust that protects it from heat loss; the so protected lava flow eventually inflates from the entry of new magma, forming a system of overlapping and interconnected lava flow lobes. Such lava flows are known as "sheet flows". Parts of the