agglomerate

sediment (unconsolidated) made up of rock fragments 20–30 mm in diameter or larger

albedo

proportion of the solar radiation reflected by a nonluminous body

albite

— see feldspar

alluvial

processes, materials, or landscapes related to streams or rivers

altiplano (Spanish)

plateau, high-altitude flat or undulating surface

andesite

volcanic rock consisting mainly of oligoclase feldspar (medium term of the isomorphous series of plagioclase feldspars) and frequently including pyroxenes and magnetite (normally without or with very little quartz)

anfractuosity

irregularity on a rock surface, intricate path

anorthite

— see feldspar

aquiclude

very low permeability rock stratum obstructing the passage of groundwater

aquitard

low permeability rock layer that slows down the passage of groundwater

argillization

processes of transformation of nonclayey minerals and rocks into clayey ones (i.e., feldspar into smectitic clays)

artesian

pressure condition of an aquifer allowing free flow of water to at least ground level

basalt

volcanic rock consisting mainly of labrador feldspar (plagioclase feldspar rich in calcium) and frequently including pyroxenes and magnetite (normally without or with very little quartz)

bomb

rounded block of lava that is ejected from a volcanic crater during eruptions

breccia

volcanic?r sedimentary rock consisting of large angular pieces in a fine-grained matrix

conglomerate

sedimentary rock (consolidated) mainly consisting of rock fragments larger than 20–30 mm in diameter (gravels, pebbles, and boulders)

cratonic

tectonically stable

dacite

volcanic rock composed of oligoclase feldspar and other associated minerals: the volcanic equivalent of granodiorites

diagenetic

changes in mineral composition and texture that take place in a sediment, mainly as a result of conditions created by burying under new layers of sediments or recent lava flows (such as increased pressure and temperature)

dolomite

a calcium and magnesium carbonate mineral; also the rock chiefly composed of this mineral

epeirogenic phenomena

large scale changes in the level of the earth crust due to which the surfaces of the continents are elevated or depressed with relatively little fracturing or folding

feldspar

group of silicate or aluminum minerals, with a three-dimensional crystalline structure (tectosilicates). The main subgroups are the plagioclases (calcium-rich term is anorthite, sodium-rich term is albite, intermediate terms are labrador and oligoclase) and the orthoclases (potassium feldspars)

ferrallitic

soil rich in iron and aluminum due to washing of other cations as a result of the long action of a humid climate. Ferrallitic soils are composed of aluminum and iron minerals such as gibbsite (aluminum hydroxide) and goethite (iron hydroxide). Kaolinite can also be present.

fersiallitic

soil rich in iron and aluminum but still conserving a substantial amount of silica. Fersiallitic soils consist mainly of smectitic clays (such as montmorillonite)

flysch

fine detritic (silty, clayey, or occasionally sandy) sedimentary rock formed during the medium stages of orogenesis in shallow coastal waters or on continental plains

gelifraction

processes of fracturing of rocks fragments by the action of ice

gibbsite

— see ferrallitic

gneisses

metamorphic rocks consisting of granite-type minerals (essentially feldspar, frequently associated are also quartz, micas, and amphibols, among others). Gneisses are formed in medium or deep metamorphic geological environments as a result of the metamorphism of clayey sedimentary or granitic rocks

goethite

— see ferrallitic

graben

depressed section of the earth’s crust bounded by faults and generally much longer than wide

horst

elevated section of the earth’s crust bounded by faults

hydraulic conductivity (K)

capacity of a geological material for allowing the flow of water

hydrological basin

area drained by a river and its tributaries

hyperpluvial zones

zones of very intense rainfall (i.e., higher than 3 000 mm/year)

kaolinite

nonexpansive clay; — see also ferrallitic

karstic

geological and geomorphological processes or features related to dissolution of carbonate minerals by water in limestone environments (main processes include enlargement of fractures and cave formation)

labrador feldspar

— see basalt

lacustrine

processes or features occurring or developed in lakes or surrounding areas under the influence of these water bodies .

lahar

mud flow of ash and water on the sides of a volcano

lapilli

small rock fragment ejected by a volcano

lentic

relating to still water

llanos (Spanish)

plains; normally used for the Colombian-Venezuelan savanna plains

lava

— see magma

magma

underground molten material, it is mainly found in volcanic regions (when it is spilled or ejected to the surface without solidification it is called lava)

massif

principal mountain mass

mica schists

— see schists

migmatites

metamorphic rocks formed by widespread injection of quartz and feldspar in the form of small dykes and formed as a result of partial and differential melting and local remobilization of molten materials

molasse

coarse-grained sedimentary rocks (chiefly conglomerates) formed in a subaerian, continental environment during the late stages of the orogenesis

montmorillonite

— see fersiallitic

oligoclase

— see feldspar

orogenesis

mountain-forming processes

orography

related to .relief

orthoclases

— see feldspar

palustrian formations

wetlands formations

pampas (Spanish)

South American grasslands of Argentina, Uruguay, and southern Brazil

phreatic eruption

stearn or hot water eruption, or a combination

phyllites

low-grade metamorphic rocks made up of mica-type minerals (such as sericite, illite, muscovite, chlorite, etc.) — see also schists

plagioclases

— see feldspar

pyroclastic

generic term used to designate volcanic rocks that are formed as a result of the accumulation and consolidation of volcanic fragments, ashes, or dust, due to gravity, gas ejection, wind, water transport, etc.

rhyolite

silica-rich volcanic rock (normally consisting of orthoclase feldspar and quartz)

sabana (Spanish)

savanna

saline intrusion

encroachment of salty water into a fresh-water aquifer

savanna

tropical grasslands

schists

low- or medium-grade metamorphic rocks composed of mica-type minerals (mainly muscovite and biotite but also sericite, illite, and chlorite). The term schist includes phyllites, mica schists, and several other metamorphic rock types

scoria

extremely vesicular lava formed as a result of eruption in the presence of gases

smectitic clays

— expansive clays; see also fersiallitic

steppe

semi-arid ecosystems characterized by low density of vegetation, normally grasses and shrub communities

syenite

— see trachyte

tuff

volcanic rock formed as a result of the consolidation of volcanic ash and dust

tectonic

internal processes moulding the various features of the earth crust

trachyte

volcanic rock made up of potassium feldspars; other minerals such as plagioclase feldspars and quartz can also be present (the igneous homologue is called syenite)

thalweg

line followed by a stream in a valley

tillite

glacial conglomerate

watershed

boundary zone between river systems, headwaters

well screen

perforated tube used to allow water to flow into a well