Pampas Onduladas lava flow have been buried by more recent lava flows. Together with the Þjórsá Lava in Iceland and the Toomba and Undara lava flows in Queensland, Australia, it is one of only a few Quaternary lava flows that reached a length of over and it has been compared to some long lava flows on Mars. Southwest from Pampas Onduladas lie the Los Carrizales lava flows, which have in part advanced to even larger distances than Pampas Onduladas but owing to a straighter course are considered to be shorter than the Pampas Onduladas lava flow, and the La Carbonilla lava flow which like Los Carrizales propagated southeastward and is located just west from the latter. Additional large lava flows are located in the western part of the field and resemble the Pampas Onduladas lava flow, such as the El Puente Formation close to the Rio Grande River of possibly recent age. Long lava flows have also been produced by volcanic centres directly south of Payún Matrú, including the long El Corcovo, Pampa de Luanco and Pampa de Ranquelcó flows. Hydrography and non-volcanic landscape Apart from the lake in the caldera, the area of Payún Matrú is largely devoid of permanent water sources, with most water sites that draw in humans being either temporary so-called "" or ephemeral. Likewise, there are no permanent rivers in the field and most of the precipitation quickly seeps into the permeable or sandy ground. The whole massif is surrounded by sandy plains, which are simply volcanic rocks covered by aeolian sediments; the plains also feature small closed basins which are also found in the lavic area. Geology West of South America, the Nazca Plate and the Antarctic Plate subduct beneath the South America Plate at a rate of , giving rise to the Andean volcanic belt. The volcanic belt is not continuous and is interrupted by gaps where the subduction is shallower and the asthenosphere between the two plates missing. North of the Payún Matrú, flat slab subduction takes place; in the past flat slab subduction occurred farther south as well and had noticeable influence on magma chemistry. In general, the mode of subduction in the region over time has been variable. There is evidence of Precambrian (older than 541 ± 0.1 million years ago) and Permian-Triassic (298.9 ±0.15 to 201.3 ±0.2 million years ago) volcanism (Choique Mahuida Formation) in the region, but a