3.7.15 Trough (Trau)
3.7.15.1 A trough is a long, narrow, negative geomorphological and/or structural form element that is delimited by steep flanks relative to its surroundings. Its flanks may be defined by faults (Figs. 9, 10).
3.7.15.2 Every trough is a basin and a depression.
3.7.15.3 Troughs are regional in size.
3.7.15.4 The structure is mappable with the help of geomorphological, geological and/or geophysical methods.
3.7.15.5 A trough may occur as an isolated, independent form element, but can also be part of a larger geomorphological and/or structural feature. A trough will often be divisible into smaller form elements.
3.7.15.6 A trough can be given a formal or an informal name in accordance with the "general rules for naming and defining geological units" (Chap. 2) and the rules for naming geological form units (Section 3.7.1). The proper name (Section 2.2.2) is placed between the words "the ... Trough" in formal names.
3.7.15.7.a A trough that can be shown to be fault-bounded, is a graben or rift (Section 3.7.16).
3.7.15.7.b A trench (grøft) is also a long, narrow, negative geomorphological and/or structural form element, but is bounded by steeper flanks relative to its surroundings than a trough. The term trench is especially used for elongate, regional, sea-floor depressions in plate tectonic contexts ("oceanic trench", dyphavsgrøft). These can be given formal or informal names.
3.7.15.7.c The term channel (renne) is used in a geomorphological context for an elongate, narrow depression, such as a marginal meltwater channel (spylerenne), in Quaternary geology. In marine geology, a channel is a long, narrow depression on the sea floor which may have a regional extent; it can be given an informal or a formal name. A regional, deep submarine channel should be called a trench, not a channel.
3.7.15.7.d Channel (kanal), used in a coastal geomorphological context, characterizes (1) a narrow strip of sea or lake separating two landmasses and connecting two large bodies of water, and (2) the deeper part of a body of water through which the main current flows, or that is most suitable for boat traffic -- usually called "renne" in Norwegian. Channels are generally given proper names.
3.7.15.7.e A canyon (gjel, juv) is a deep, steep-sided valley formed by river or submarine erosion (submarine canyon, undersjøisk gjel). A gorge resembles a canyon, but is generally smaller. Prominent canyons and gorges often have local proper names.
3.7.15.8 Examples: The Bamble Trough (Bambletrauet) is a structural trough (Rønnevik et al. 1975b). Examples of plate tectonic ocean trenches are the Mariane Trench (Marianegrøfta), Japan Trench (Japangrøfta) and Peru--Chile Trench (Peru--Chile-grøfta). The Norwegian Trench (Norskerenna) is an example of a submarine channel, whilst Jutulhogget in east central Norway and Savco, near Alta, in northern Norway are examples of canyons (gjel).
3.7.15.9 Key reference: Bates & Jackson (1980).
