Key Concepts in Geology and Landforms
**Contour Lines**
Contour lines are lines on a map connecting all points having equal status and height or elevation. Contour maps are usually printed in sienna color for the field and blue for glaciers, deep seas, and lakes.
**Delta**
A delta is the triangular area formed at the mouth of a river by sediment deposited as the stream disappears. It is composed of arms or “pipes” of the river that separate the islands that have been deposited by sediments carried by the river to reach the sea, ocean, or lake.
**Erosion**
Erosion is the process of removal or wearing away of intact soil (rock) by the action of exogenous geological processes such as surface water flows, glacial ice, wind, or the action of living organisms.
**Fault**
A fault is a fracture of the Earth’s crust caused by tectonic stress that causes displacement of a portion of the Earth’s crust over the other, both vertically and horizontally.
**Graben (Rift Valley)**
A rift valley or graben is a long depression limited on both sides by parallel raised faults (horsts) from which the field has collapsed as a result of internal forces.
**Horst**
A horst is an elevated region bounded by two normal, parallel faults.
**Fold**
A fold is a deformation of rocks, usually sedimentary, in which horizontal elements, such as strata or cleavage planes (in the case of metamorphic rocks), are curved, forming waves elongated and more or less parallel. Folds are caused by compression stresses on the rocks that do not break.
**Volcanism**
Volcanism occurs when the molten material inside the Earth comes to the surface through cracks, crevices, and holes. This material coming out is called lava, which is characterized by rapidly cooling and releasing its dissolved gases. Moreover, some of the high-temperature minerals formed are built and separated from the magma. According to the viscosity of the material, the characteristics of the volcanic eruption vary.
**Butte**
A butte is a residual relief comprising a horizontal hilltop topped by a layer of hard and soft materials on its flanks. It is typical of differential erosion on flat or slightly inclined layers formed by alternately hard and soft materials. They are separated from the river network platforms (tables or wetlands) that are reduced and eventually become isolated hills, such as watershed mesetas of the depressions of the Ebro and Guadalquivir.
**Tectonic Style**
Tectonic style is the set of characters that may represent a tectonic structure and the deformation mechanisms that produce it: faulting (Appalachian relief) or folding (Jurassic relief).
**Glaciers**
Glaciers are a climate process by which, due to a general cooling of the planet, an expansion of ice occurs over large areas of the land surface. In the present Quaternary era, there have been four glacial periods corresponding to interglacial periods. We are currently in a post-glacial period (the Holocene).
**Plateau**
A plateau is a basic unit of relief on the Peninsula. It is a largely flat area of high average altitude, remaining from an old solid that emerged in the Hercynian orogeny of the Primary Era, which was destroyed by erosion. In the Tertiary, it was deformed and largely destroyed during the Alpine orogeny, which gave rise to the interior mountain ranges, sedimentary basins, and mountain ridges.
**Orogeny**
Orogeny is the set of geological processes, both external and internal, that cause the formation and folding of mountains. This whole process is closely attached to plate tectonics.
**Moorland**
A moorland is a flat and high surface, surmounted by a limestone layer more resistant to erosion. River erosion carves valleys that cut and separate smaller tables. On the Peninsula, they are located in the northern and eastern basin of the central plains in the north and east of the southern sub-plateau.
**Countryside**
A countryside is a low, gently rolling plain, crossed by rivers. In Spain, they are characteristic of sedimentary basins and the depression of the Guadalquivir.
**Peneplain**
A peneplain is a large, gently undulating surface of erosion with a low slope, the result of a long cycle in which erosion has been quiet at times, causing widespread razing of relief.
**Scree**
Scree is an accumulation in a tank, plains, and gentle slopes, formed by rocky material (from the erosion of quartzite) plastered on clay (from the decomposition of the slates).
**Appalachian Relief**
Appalachian relief is a form of relief arising from the effects of differential erosion, leaving the hard layers that form the peaks highlighted and eroding the soft tissues that form the valleys through which the river network is embedded.
**Karst Landforms**
Karst landforms are a set of topographic features in limestone areas, caused by the action of acidic water (with carbon dioxide) that dissolves the limestone. The most typical are sinkholes, dolines, poljes, caves, and chasms.
**Base**
A base is a large group of ancient lands, formed of granite rocks, on which modern sedimentary materials rest. The bases are usually very long and behave like hard material, which breaks before folding.