page_title: Cerro Blanco (volcano)
section_title: Aeolian landscapes
hierarchical_section_title: Cerro Blanco (volcano) / Geography and geomorphology / Aeolian landscapes
caption_attribution_description: Español: Campo de Piedra Pómez, Catamarca, Argentina
context_page_description: Cerro Blanco is a caldera in the Andes of the Catamarca Province in Argentina. Part of the Central Volcanic Zone of the Andes, it is a volcano collapse structure located at an altitude of 4,670 metres in a depression. The caldera is associated with a less well defined caldera to the south and several lava domes.
  The caldera has been active for the last eight million years and eruptions have created several ignimbrites. A recent eruption occurred 73,000 years ago and formed the Campo de la Piedra Pómez ignimbrite layer. About 2,300 ± 160 BCE, the largest volcanic eruption of the Central Andes with a VEI 7 occurred at Cerro Blanco, forming the most recent caldera as well as thick ignimbrite layers. Over 170 cubic kilometres of tephra were erupted then. The volcano is dormant since then with some deformation and geothermal activity. A major future eruption would put local communities to the south at risk.
  The volcano is also known for giant ripple marks that have formed on its ignimbrite fields. Persistent wind action on the ground has shifted gravel and sand, forming wave-like structures. These ripple marks have heights up to 1 metre and are separated by distances up to 30 metres.
context_section_description: One of the most spectacular aeolian landscapes is found at Cerro Blanco, where large wind-formed ripple marks occur. These ripples cover Cerro Blanco ignimbrites and reach heights of 2.3 metres (7 ft 7 in) and wavelengths of 43 metres (141 ft), making them the largest ripples known on Earth and comparable to similar ripple fields on Mars. Wind-driven erosion of ignimbrites has generated the ripples, which consist of gravel, pebbles and sand and are covered with gravel. Smaller gravelly ripples lie atop the larger ripples and troughs and there are intermediate sized forms (0.6–0.8 metres (2 ft 0 in–2 ft 7 in) high); they may be precursors to the large ripples and make up most of the ripples in the fields. Their wind-driven movement is fast enough that trails abandoned four years before are already partly covered with them.  
  The ripple marks cover areas of about 150 square kilometres (58 sq mi) or 600 square kilometres (230 sq mi) in the Carachipampa and 80 square kilometres (31 sq mi) or 127 square kilometres (49 sq mi) in the Purulla valley. A field of large ripples covers an area of 8 square kilometres (3.1 sq mi) in the Purulla valley and is accompanied by yardangs; this field is also the place where the largest ripples occur. 
  Various wind-dependent mechanisms have been proposed to explain their large size, including the presence of roll vortexes, Helmholtz instability-like phenomena, atmospheric gravity waves or creep-like movement when pumice fragments and sand are lifted from the ground by wind and fall back. The latter view envisages that undulating terrain triggers the development of ripples through the accumulation of gravel and sand at such undulations. Their formation appears to be influenced by whether the rock material available can be moved by wind while a role of the bedrock structure or the size of the material is controversial.
  Wind has also formed demoiselles and yardangs in the ignimbrites. These are particularly well expressed in the Campo de Piedra Pomez area southeast of the Carachipampa valley, a 25 by 5 kilometres (15.5 mi × 3.1 mi) area where yardangs, hoodoos and wind-exposed cliffs create a majestic landscape. The structures reach widths of 2–20 metres (6 ft 7 in–65 ft 7 in) and heights of 10 metres (33 ft) and form an array-like assembly. They have fluted surfaces. The yardangs appear to form beginning from a fumarolic vent where the rock has been hardened, and eventually develop through a series of early, intermediate and late yardang forms as wind and wind-transported particles erode the rocks. Exposed rocks are often covered with brown, orange or beige desert varnish.
  Bedrock ridges are cut into ignimbrites of the Incahuasi valley. This terrain gradually leads over into the megaripple-covered surface through an increased gravel cover. The development of these megaripples appears to have been influenced by the underlying bedrock ridges which move alongside with the overlying ripples. These bedrock ridges are formed through erosion by wind and by wind-transported particles, it is not clear how they are then exposed from the ripples. Additional aeolian landforms in the region are known and include ventifacts and so-called "aeolian rat tails"; these are small structures which form when erosion-resistant rock fragments slow wind erosion in their lee, thus leaving a tail-like area where less rock is eroded.
  The Campo de Piedra Pómez makes up the Campo de Piedra Pómez Natural Protected Area, a protected area of Catamarca Province. It was among the finalists in the "Seven Wonders of Argentina" contest.
caption: Campo de Piedra Pómez yardangs
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