Silt is a solid, dust-like sediment that water, ice, and wind transport and deposit.
Silt
is made up of rock and mineral particles that are larger than clay but smaller than sand. Individual
silt
particles
are so small that they are difficult to see. To be classified as
silt
, a
particle
must be less than .005 centimeters (.002 inches) across.
Silt
is found in soil, along with other types of
sediment
such as
clay
,
sand
, and gravel.
Silty
soil
is slippery when wet, not grainy or
rocky
. The
soil
itself can be called
silt
if its
silt
content is greater than 80 percent. When
deposits
of
silt
are compressed and the grains are pressed together,
rocks
such as siltstone form.
Silt
is created when
rock
is eroded, or worn away, by water and ice. As flowing water
transports tiny
rock
fragments, they scrape against the sides and bottoms of stream beds, chipping away more
rock
. The
particles
grind against each other, becoming smaller and smaller until they are
silt
-size. Glaciers can also
erode
rock
particles
to create
silt
. Finally,
wind
can
trans
port
rock
particles
through a canyon or across a landscape, forcing the
particles
to grind against the
canyon
wall or one another. All three processes create
silt
.
Silt
can change
landscapes
. For example,
silt
settles in still water. So,
deposits
of
silt
slowly fill in places like wetlands, lakes, and harbors. Floods
deposit
silt
along river banks and on flood plains. Deltas develop where rivers
deposit
silt
as they empty into another body of water. About 60 percent of the Mississippi
River
Delta
is made up of
silt
.
In some parts of the world,
windblown
silt
blankets the land. Such
deposits
of
silt
are known as loess.
Loess
landscapes
, such as the Great Plains, are usually a sign of past glacial activity.
Many species of organisms thrive in slick,
silty
soil
. Lotus plants take root in muddy,
silty
wetlands
, but their large, showy flowers blossom above water. The lotus is an im
portant
symbol in Hindu, Buddhist, and ancient Egyptian religions. The lotus is the national flower of India and Vietnam.
Many species of frog hibernate during the cold winter by burying themselves in a layer of soft
silt
at the bottom of a
lake
or pond. Water at the bottom of a body of water does not freeze, and the
silt
provides some insulation, or warmth, for the animal.
Silty
soil
is usually more fertile than other types of
soil
, meaning it is good for growing crops.
Silt
promotes water retention and air circulation. Too much
clay
can make
soil
too stiff for plants to
thrive
. In many parts of the world, agriculture has
thrived
in
river
deltas
, where
silt
deposits
are rich, and along the sides of
rivers
where annual
floods
replenish
silt
. The Nile
River
Delta
in Egypt is one example of an extremely
fertile
area where farmers have been harvesting
crops
for thou
sands
of years.
When there aren't enough trees,
rocks
, or other materials to prevent erosion,
silt
can accumulate quickly. Too much
silt
can upset some ecosystems.
"Slash and burn"
agriculture
, for instance, upsets the
ecosystem
by removing trees. Agricultural
soil
is washed away into
rivers
, and nearby waterways are clogged with
silt
. Animals and plants that have adapted to live in moderately
silty
soil
are forced to find a new niche in order to survive. The
river
habitats of some organisms in the Amazon
River
, such as the pink Amazon River dolphin, also called the boto, are threatened.
River
dolphins cannot locate prey as well in
silty
water.
Agricultural and in
dustrial
runoff can also
clog
ecosystems
with
silt
and other
sediment
. In areas that use chemical fertilizers,
runoff
can make
silt
toxic.
Toxic
silt
can poison
rivers
,
lakes
, and streams.
Silt
can also be made
toxic
by exposure to in
dustrial
chemicals from ships, making the
silt
at the bottom of
ports
and
harbors
especially at risk. When the city of Melbourne, Australia, decided to deepen its
harbor
in 2008, many people worried that disturbing millions of tons of
silt
, filled with chemicals like arsenic and lead, would threaten the waterway's
ecosystem
.
FAQs
Silty soil is slippery when wet, not grainy or rocky. The soil itself can be called silt if its silt content is greater than 80 percent. When deposits of silt are compressed and the grains are pressed together, rocks such as siltstone form. Silt is created when rock is eroded, or worn away, by water and ice.
What is the simple definition of silt? ›
Silt is the fine bits of clay and sand that become sediment settling at the bottom of a river or lake. If there's a lot of silt flowing in a river, it looks murky. Silt is the super-fine dirt that you might see at the bottom of a lake or river.
What is silt good for? ›
The quartz particles in silt do not themselves provide nutrients, but they promote excellent soil structure, and silt-sized particles of other minerals, present in smaller amounts, provide the necessary nutrients.
What is silt and why is it a problem? ›
Silt refers to the dirt, soil, or sediment that is carried and deposited by our water. While some silt in water is normal and healthy, many additional tons of silt find their way to our water every year, negatively impacting water quality.
Why is silt soil bad? ›
The greater surface area relative to volume can result in long-lasting water retention. This in turn may causes silty soil to expand and shift. This lack of stability means that structures on silty soil are subject to repeated and prolonged stress, potentially resulting in structural damages.
Is silt the same as topsoil? ›
The topsoil layer is a mixture of sand, silt, clay, and broken-down organic matter, called humus. Humus is a rich, highly decomposed organic matter mostly made from dead plants, crunched-up leaves, dead insects, and twigs.
How to fix silt soil? ›
Silty soils contain small irregularly shaped particles of weathered rock, which means they are usually quite dense and have relatively small pore spaces and poor drainage. They tend to be more fertile than either sandy or clayey soils. To improve silty soil: Add at least 1 inch of organic matter each year.
What grows well in silt? ›
Shallow-rooted vegetables like lettuce, onion, broccoli, and other related brassicas are good options. Nitrogen-fixing vegetables like peas and legumes are also great to further amend your soil. A plot with silty soil would be well suited for a Three Sisters garden with corn, beans, and squash.
Is Pond silt good for garden? ›
As long as your pond isn't having any trouble that has required use of chemicals or salt, all those living microbes that you've scraped off the top and bottom are perfectly suited as a fertilizer.
Is silt harmful to humans? ›
Always assume that debris and flood water (and therefore silt) is contaminated with farm run-off, chemicals, or sewage. Contaminated debris, flood water, and silt can make you sick. You need to take precautions when you are disturbing silt, debris, or floodwater when working.
Composting and Soil Amendments:
If the silt contains organic matter, it can be composted with other materials to create nutrient-rich compost that can be used in gardening and landscaping.
Is silt good for growing grass? ›
Moisture-loving plants in particular tend to thrive in silt soil. Vines, lush grasses and richly colored flowers are some examples of plants that are especially well-suited for silt soil.
What grows in silt soil? ›
Shallow-rooted vegetables like lettuce, onion, broccoli, and other related brassicas are good options. Nitrogen-fixing vegetables like peas and legumes are also great to further amend your soil. A plot with silty soil would be well suited for a Three Sisters garden with corn, beans, and squash.
Is silt better than sand? ›
Silt is more worn down and has particles that are not as strong as sand, so it is more prone to loosing small amounts of mineral nutrients from each particle amounting to a lot more minerals being available to your plants.
What is the difference between silt and mud? ›
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz ,it is like mud or clay or small rocks deposited by a river or lake. Mud is a mixture of water and some combination of soil, silt, and clay.
