|I can see different layers of soil emerging from the Ocean at the beach when there is low tide. How were these layers formed?
|Question Date: 2011-12-02|
These layers are called sedimentary layers. They develop as waves wash ashore and retreat; when the wave retreats it deposits its load of suspended sediment as a single layer. Because different size grains settle at different rates and because minerals can have different densities, often a layer will exhibit internal gradation in terms of size/density. Then another wave washes up and the process is repeated again and again. Sometimes previously deposited layers get eroded...sometimes not. When the layers get buried they can be preserved for millions, even billions, of years. The loose layers will lithify (is the process in which sediments compact under pressure) and become indurated rock.
I'm not sure I understand the question exactly, but here goes:
At low tide, sometimes rock layers underneath the beach sand become visible.Along the Santa Barbara coast, these layers are usually the 16- to 6-million-year-old Monterey Formation. This rock formation is the result of the accumulation of hundreds of feet of sediment (sand, silt and clay; or, the "brown stuff carried by rivers"). Over millions of years, the sediment carried by rivers to the ocean was deposited in basins like the Santa Barbara channel (the stretch of ocean between Santa Barbara and the Channel Islands). These layers got buried deeper and deeper by more and more sediment, eventually making this sediment more compact and turning it into a hard rock.
Millions of years later, these rock layers have been brought back up to sea level because of tectonic forces. These forces not only brought the rock layers up to the surface, they also folded and tilted them. Erosion due breaking waves erode the coastal cliffs backwards, leaving a nearly flat surface of rock shallowly buried by beach sand. When the tide is low enough, these folded, tilted rock layers become visible.
Hope these answers help!
The different layers you see are different sized sand particles that have been separated by wave energy. Moving water has energy the faster the water moves, the more energy it has. We can think of very fast moving water as being like a very strong person that can move larger things. When a wave crashes at the beach, it moves very fast and carries many different sized particles of sand with it. As the wave moves toward the beach, it slows down, has less energy, and drops some of the larger pieces of sand on the bottom. As the water continues to slow down it loses energy and continues to drop smaller and smaller pieces of sand. This is called natural sorting.
A great way to see how this works without waves is to dig a hole in the sand. You will see many different layers of sand, dark in some places and light in others. The dark layers are the smallest pieces of sand; the light colored layers are the larger, heavier pieces of sand. So why are they all in the same place in the hole? Tides! At high tide, the water can carry larger particles of sand farther up the beach; at low tide the water doesnt move as far along the beach so only the smallest particles of sand make it up the beach The layers you will see in the hole you dig will tell you a brief history of the beach and its tides. If the sand at the top is dark in color, then you know there was just a low tide and the tide must be coming in. If the sand at the top layer of the hole is light in color, then you know there was just a high tide and the tide must be going out. Pretty cool, right?
Good question! However, there are two possible answers, depending on what you are looking at: do you mean different colors of sand at the beach, or different colors of the material of the sea-cliffs along the beach?
If you're looking at the sand: what you are seeing is different layers of beach sediments laid down under different conditions, such as storms versus fair weather. If you're looking at the cliffs, then you're seeing what those layers of the beach will eventually become: rocks that are part of the Earth's crust that will one day be ground back into what they came from: sand and sediment. This is a part of what is called the "rock cycle".
The different layers of "soil" your are observing at the beach can be formed in numerous ways. First it is important to correctly identify the material you are seeing at the beach. Depending on the material will determine the process responsible for the materials formation.
Is it actually a soil, are there roots growing in the medium, can you distinguish different horizontal layers of distinct color and texture? If so then you are likely looking at a soil. Soils are formed from the weathering (chemical and/or physical) breakdown of rock and sediment. The major components of soil include: sand, silt, clay, organic matter, and pore spaces. The factors that control soil formation and type include: climate, organisms, relief (landscape), parent material, and time. For example with all above factors being equal, wetter climates exhibit thicker soils compared to soils formed in arid environments.
The different colors and layers reflect differences in the layers' permeability (ability of water to flow through a medium), texture (determined by percent sand, silt, clay, or organic matter), and/or the minerals in each layer. As water flows through the different layers, organisms break-down organic matter, and organisms (worms, moles, roots, etc) stir up the soil chemical and physical reactions take place to alter the texture and color of each layer. Think of the different layers as different ecosystems zones (e.g. a desert versus a rainforest).
Through time the soil is formed however at the same time waves, tides, water, and wind eroded the shoreline. The soil is being exposed as waves and tides erode the coastline and expose fresh surfaces of the soil.
If you are not looking at a soil you may be looking at sedimentary rock (deposits formed in ancient environments and later hardened) or a modern depositional environment (e.g. a beach deposit or river deposit).
To answer your question more fully one must know more about the layers you are seeing. Look closely at the layers, what is the material composed of, what is its color and hardness? What is the inclination of the layers? Can you see any roots or fossils? Are there any structures internal to the layers (can you see internal layers within the larger layers)?.
A myriad of different process may be at play. Look at the environments around you today; the creeks that run into the ocean, the lagoons that line the coastline, the waves that push sand about at the coast, the squirrels that dig into the soil, or the wind that blows dust and sand into dunes. Try and find modern environments where you can see material (sediments) being deposited then compare those deposits with the ones you see at the beach. You may be surprised at what you can find out.
What you might be seeing at low tide are layers of sand and silt and mud that were deposited during higher tide levels. Rivers bring sand and silt and mud into the ocean, and then these particles settle out on the seafloor, forming a layer of sediment. When the tide goes out, these layers are then revealed.
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