Roca Remolinos (lit. ''"Eddies Rock"'') is a submarine hill in

Chacao Channel The Chacao Channel () is located in Los Lagos Region, Chile and separates Chiloé Island from mainland Chile. The channel is about 40 km long and 4 km wide and connects the Pacific Ocean and Gulf of Ancud. The channel was created during the Quat ...

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

, notorious for being a major hazard for traffic along the channel. With its highest point at 20 m below sea level, Roca Remolinos does not break the surface during ordinary low tides, but its top can occasionally be seen during extremely low tides. It is located at the narrowest part of the channel, about 700 m from the nearest shore (the southern one). Its northern slope reaches 16° while its southern one reaches 14°. The rock composition varies: four different horizontal layers have been identified, all of which are made of combinations of

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

and

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

cemented by

ferric oxide Iron(III) oxide or ferric oxide is the inorganic compound with the formula . It occurs in nature as the mineral hematite, which serves as the primary source of iron for the steel industry. It is also known as red iron oxide, especially when us ...

.Syngros, K.; Dobry, R.; Leventis, G.E. Chacao Channel Bridge–the Design Challenges. In Proceedings of the International Conference on Case Histories in Geotechnical Engineering—Sixth International Conference on Case Histories in Geotechnical Engineering, Arlington, VA, USA, 11–16 August 2008. The uppermost 40 m is a

caprock Caprock or cap rock is a hard, resistant, and impermeable layer of rock that overlies and protects a reservoir of softer organic material, similar to the crust on a pie where the crust (caprock) prevents leakage of the soft filling (softer materia ...

layer made of medium to fine sandstone and is

tuffite Tuffite is a tuff containing both pyroclastic and detrital materials, but predominantly pyroclasts. According to the IUGS definition, tuffite contains 75% to 25% volcanic (epiclastic) material. There are several classifications that define tuffi ...

. Below this layer comes 35 m of medium sandstone which in parts has low cementation levels. Below this there are 30 m of well-cemented silt. Under the well-cemented silt there is at least 20 m of densely compacted medium sand which is partly cemented. When there are strong tidal currents in Chacao Channel the rock creates

eddies In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid is in a turbulent flow regime. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object. Fluid ...

, drawing objects to it. Roca Remolinos was studied by

Chilean Navy The Chilean Navy () is the naval warfare service branch of the Chilean Armed Forces. It is under the Ministry of National Defense (Chile), Ministry of National Defense. Its headquarters are at Edificio Armada de Chile, Valparaiso. History Ori ...

officer

Francisco Hudson Punta Arenas by sea from Ancud, and in orange Hudson's proposed route. The red dot shows the 20 km wide Ofqui Isthmus the only obstacle that makes this route intransitable. --> Francisco Hudson Cárdenas (July 1, 1826 in Curaco de Vélez, Chile – ...

in the 19th century. In early planning Chacao Channel bridge was not planned to have a central tower, but it was redesigned to make use of Roca Remolinos for installing a central tower and cut thus the span in half. Before the final decision, Roca Remolinos was investigated for its capability to support a tower. As of 2023 the central tower is being built on top of Roca Remolinos. Puente Chacao

References

Landforms of Los Lagos Region Chiloé Archipelago Landforms of Chile Coasts of Los Lagos Region Individual rocks Landforms of the Pacific Ocean Sandstone Siltstone {{LosLagos-geo-stub