Sediment

Cobbles on a beach
River Rhône flowing into Lake Geneva. Sediments make the water appear brownish-grey; they are an indicator of increased water runoff, land degradation, erosion due to intensive industrialized land use, land sealing, and poor soil management.

Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice, and/or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation and if buried, may eventually become sandstone and siltstone (sedimentary rocks).

Sediments are most often transported by water (fluvial processes), but also wind (aeolian processes) and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments.

Classification

Sediment in the Gulf of Mexico
Sediment off the Yucatán Peninsula

Sediment can be classified based on its grain size and/or its composition.

Grain size

Sediment size is measured on a log base 2 scale, called the "Phi" scale, which classifies particles by size from "colloid" to "booulder".


φ scale Size range
(metric)
Size range
(inches)
Aggregate class
(Wentworth)
Other names
< -8 > 256 mm > 10.1 in Boulder
-6 to -8 64–256 mm 2.5–10.1 in Cobble
-5 to -6 32–64 mm 1.26–2.5 in Very coarse gravel Pebble
-4 to -5 16–32 mm 0.63–1.26 in Coarse gravel Pebble
-3 to -4 8–16 mm 0.31–0.63 in Medium gravel Pebble
-2 to -3 4–8 mm 0.157–0.31 in Fine gravel Pebble
-1 to -2 2–4 mm 0.079–0.157 in Very fine gravel Granule
0 to -1 1–2 mm 0.039–0.079 in Very coarse sand
1 to 0 0.5–1 mm 0.020–0.039 in Coarse sand
2 to 1 0.25–0.5 mm 0.010–0.020 in Medium sand
3 to 2 125–250 µm 0.0049–0.010 in Fine sand
4 to 3 62.5–125 µm 0.0025–0.0049 in Very fine sand
8 to 4 3.9–62.5 µm 0.00015–0.0025 in Silt Mud
> 8 < 3.9 µm < 0.00015 in Clay Mud
>10 < 1 µm < 0.000039 in Colloid Mud

Composition

Composition of sediment can be measured in terms of:

This leads to an ambiguity in which clay can be used as both a size-range and a composition (see clay minerals).

Other Languages
Afrikaans: Sediment
العربية: راسب
aragonés: Sedimento
বাংলা: পলল
беларуская (тарашкевіца)‎: Наносы
भोजपुरी: सेडिमेंट
български: Нанос
bosanski: Sedimenti
català: Sediment
čeština: Sediment
dansk: Sediment
eesti: Sete
Ελληνικά: Ίζημα
español: Sedimento
Esperanto: Sedimento
euskara: Sedimentu
فارسی: رسوب
français: Sédiment
galego: Sedimento
한국어: 퇴적물
Հայերեն: Ողողատ
hrvatski: Sedimenti
íslenska: Set
italiano: Sedimento
қазақша: Тосқындар
Kreyòl ayisyen: Sediman
Latina: Sedimentum
lumbaart: Sediment
Nederlands: Sediment
日本語: 堆積物
norsk: Sediment
norsk nynorsk: Sediment
occitan: Sediment
ਪੰਜਾਬੀ: ਫੋਗ
polski: Osady
português: Sedimento
română: Sediment
русский: Наносы
Scots: Sediment
Simple English: Sediment
slovenčina: Sediment
српски / srpski: Седимент
srpskohrvatski / српскохрватски: Sedimenti
suomi: Sedimentti
Tagalog: Latak
ไทย: ตะกอน
українська: Відклад
Tiếng Việt: Trầm tích
粵語: 沉積物
中文: 沉積物