How do large rocks become smaller

As its name implies, honeycomb weathering describes rock formations with hundreds or even thousands of pits formed by the growth of salt crystals.

Honeycomb weathering is common in coastal areas, where sea sprays constantly force rocks to interact with salts. Haloclasty is not limited to coastal landscapes. Salt upwelling , the geologic process in which underground salt dome s expand, can contribute to weathering of the overlying rock. Structures in the ancient city of Petra, Jordan, were made unstable and often collapsed due to salt upwelling from the ground below. Plants and animals can be agents of mechanical weathering. The seed of a tree may sprout in soil that has collected in a cracked rock.

As the root s grow, they widen the cracks, eventually breaking the rock into pieces. Over time, trees can break apart even large rocks. Even small plants, such as mosses, can enlarge tiny cracks as they grow. Animals that tunnel underground, such as moles and prairie dogs, also work to break apart rock and soil. Other animals dig and trample rock aboveground, causing rock to slowly crumble. Chemical weathering changes the molecular structure of rocks and soil.

For instance, carbon dioxide from the air or soil sometimes combines with water in a process called carbonation. This produces a weak acid, called carbonic acid , that can dissolve rock. Carbonic acid is especially effective at dissolving limestone. When carbonic acid seeps through limestone underground, it can open up huge cracks or hollow out vast networks of cave s.

Carlsbad Caverns National Park, in the U. The largest is called the Big Room. With an area of about 33, square meters , square feet , the Big Room is the size of six football fields. Sometimes, chemical weathering dissolves large portions of limestone or other rock on the surface of the Earth to form a landscape called karst. In these areas, the surface rock is pockmarked with holes, sinkhole s, and caves. Hundreds of slender, sharp towers of weathered limestone rise from the landscape.

Another type of chemical weathering works on rocks that contain iron. These rocks turn to rust in a process called oxidation. Rust is a compound created by the interaction of oxygen and iron in the presence of water. As rust expands, it weakens rock and helps break it apart. Hydration is a form of chemical weathering in which the chemical bond s of the mineral are changed as it interacts with water. One instance of hydration occurs as the mineral anhydrite reacts with groundwater. The water transforms anhydrite into gypsum , one of the most common minerals on Earth.

Another familiar form of chemical weathering is hydrolysis. In the process of hydrolysis, a new solution a mixture of two or more substances is formed as chemicals in rock interact with water. In many rocks, for example, sodium minerals interact with water to form a saltwater solution. Hydration and hydrolysis contribute to flared slope s, another dramatic example of a landscape formed by weathering and erosion. Living or once-living organisms can also be agents of chemical weathering. The decay ing remains of plants and some fungi form carbonic acid, which can weaken and dissolve rock.

Some bacteria can weather rock in order to access nutrient s such as magnesium or potassium. Clay minerals, including quartz , are among the most common byproduct s of chemical weathering. For example, certain kinds of air pollution increase the rate of weathering.

Burning coal , natural gas , and petroleum releases chemicals such as nitrogen oxide and sulfur dioxide into the atmosphere. When these chemicals combine with sunlight and moisture, they change into acids. Together with erosion, tall mountains turn into hills and even plains. No human being can watch for millions of years as mountains are built, nor can anyone watch as those same mountains gradually are worn away. But imagine a new sidewalk or road. The new road is smooth and even.

Over hundreds of years, it will completely disappear, but what happens over one year? What changes would you see figure 1? What forces of weathering wear down that road, or rocks or mountains over time? Follow this link to view some animations of different types of weathering processes.

Mechanical weathering also called physical weathering breaks rock into smaller pieces. These smaller pieces are just like the bigger rock, just smaller.

That means the rock has changed physically without changing its composition. The smaller pieces have the same minerals, in just the same proportions as the original rock. There are many ways that rocks can be broken apart into smaller pieces. Ice wedging is the main form of mechanical weathering in any climate that regularly cycles above and below the freezing point figure 2. Ice wedging works quickly, breaking apart rocks in areas with temperatures that cycle above and below freezing in the day and night, and also that cycle above and below freezing with the seasons.

Ice wedging breaks apart so much rock that large piles of broken rock are seen at the base of a hillside, as rock fragments separate and tumble down. Abrasion is another form of mechanical weathering. In abrasion, one rock bumps against another rock. Figure 3. Rocks on a beach are worn down by abrasion as passing waves cause them to strike each other. Abrasion makes rocks with sharp or jagged edges smooth and round.

If you have ever collected beach glass or cobbles from a stream, you have witnessed the work of abrasion figure 3. Now that you know what mechanical weathering is, can you think of other ways it could happen? Plants and animals can do the work of mechanical weathering figure 4. Burrowing animals can also break apart rock as they dig for food or to make living spaces for themselves.

Figure 4. Mechanical weathering increases the rate of chemical weathering. As rock breaks into smaller pieces, the surface area of the pieces increases figure 5. With more surfaces exposed, there are more surfaces on which chemical weathering can occur. Figure 5. Mechanical weathering may increase the rate of chemical weathering. Here are some initial questions that your students can discuss, in pairs, in groups, and as a whole class: What happens when rocks smash into each other?

What might cause rocks to smash or grind against each other? Do all rocks break apart in the same way? Some rocks can have rough edges while others are quite smooth?

What might create a smooth rock? Have your students share their ideas with the class and record them as a list on the flipchart. Exploring the Concept Provide the materials to the students.

Instruct students to cover their desktops with paper. Have students examine the sugar cubes with the magnifying glasses.

Students should record their observations on the observation sheet provided. They can either draw or describe the sugar cubes. Ask students to predict how the sugar cubes will change after they have been shaken inside the container for 1 minute. Students should record their predictions on the observation sheet. Students shake the container with the sugar cubes inside for one minute. Instruct students to open their containers and to poor the materials inside onto their desktops. Students use their magnifying glasses to re-examine the sugar cubes.

They should record their observations on the observation sheet. Ask students to put the sugar cubes back into the container along with the gravel provided. Ask them to close the containers with the lids. Ask students to predict how the sugar cubes will change after they have been shaken inside the container with the gravel for 1 minute. Students shake the container a second time for 1 minute with the sugar cubes and gravel inside.

Ask students to develop a conclusion about why the cubes changed as they did after each shaking. Hold a class discussion about what the students observed. Ask students the following questions. How did the sugar cubes change after the first shaking? What may have caused these changes? Did the second shaking with the gravel cause the sugar cubes to look more worn? How did your predictions compare to your results. Introduce to students the term weathering.

Ask them the following questions: What might cause rocks in nature to be shaken together much like how you shook the sugar cubes together with the gravel? For example, if a section of underlying sediment firms up, this may be enough to create a form a layer that is dissimilar from the overlying sediment.

Each layer is called a bed A specific layer of rock with identifiable properties. As would be expected, bed A specific layer of rock with identifiable properties. Technically, a bed A specific layer of rock with identifiable properties.

A layer thinner than 1 cm 0. Varves are bedding planes created when laminae and bed A specific layer of rock with identifiable properties. Varves are valuable geologic records of climatic histories, especially those found in lakes and glacial deposits. Graded bedding refers to a sequence of increasingly coarse- or fine-grained sediment layers.

Graded bedding often develops when sediment deposition occurs in an environment of decreasing energy. A Bouma sequence is graded bedding observed in clastic rock called turbidite. Bouma sequence bed A specific layer of rock with identifiable properties. These subsea density flows begin when sediment is stirred up by an energetic process and becomes a dense slurry of mixed grains. The sediment flow courses downward through submarine channels and canyons due to gravity acting on the density difference between the denser slurry and less dense surrounding seawater.

As the flow reaches deeper ocean basins it slows down, loses energy, and deposits sediment in a Bouma sequence of coarse grains first, followed by increasingly finer grains see figure.

In fluid systems, such as moving water or wind, sand is the most easily transported and deposited sediment grain. Smaller particles like silt and clay are less movable by fluid systems because the tiny grains are chemically attracted to each other and stick to the underlying sediment.

Under higher flow rates, the fine silt and clay sediment tends to stay in place and the larger sand grains get picked up and moved.

Bedforms are sedimentary structures created by fluid systems working on sandy sediment. Grain size , flow velocity, and flow regime or pattern interact to produce bedforms having unique, identifiable physical characteristics. Flow regimes are divided into upper and lower regimes, which are further divided into uppermost, upper, lower, and lowermost parts. The table below shows bedforms and their associated flow regimes. For example, the dune A large pile of sediment, deposited perpendicular to flow.

Internal bedding in dunes dips toward flow direction i. Formed in the upper part of the lower flow regime. Plane bed A specific layer of rock with identifiable properties. The flat, parallel layers form as sandy sediment piles and move on top of layers below.

Even non-flowing fluid systems, such as lakes, can produce sediment plane bed A specific layer of rock with identifiable properties. They may look identical to lower-flow-regime bed A specific layer of rock with identifiable properties. Ripples are known by several names: ripple marks, ripple cross bed A specific layer of rock with identifiable properties. The ridges or undulations in the bed A specific layer of rock with identifiable properties.

With the exception of dune A large pile of sediment, deposited perpendicular to flow. Occasionally, large flows like glacial lake outbursts, can produce ripples as tall as 20 m 66 ft. First scientifically described by Hertha Ayrton, ripple shapes are determined by flow type and can be straight-crested, sinuous, or complex. Asymmetrical ripples form in a unidirectional flow. Symmetrical ripples are the result of an oscillating back-and-forth flow typical of intertidal swash zones. Climbing ripples are created from high sedimentation rates and appear as overlapping layers of ripple shapes see figure.

Cross bedding happens when ripples or dune A large pile of sediment, deposited perpendicular to flow. Desert sand dune A large pile of sediment, deposited perpendicular to flow. British geologist Agnold considered only Barchan and linear Seif dune A large pile of sediment, deposited perpendicular to flow. Other workers have recognized transverse and star dunes as well as parabolic and linear dunes anchored by plants that are common in coastal areas as other types of dune A large pile of sediment, deposited perpendicular to flow.

The biggest difference between river dune A large pile of sediment, deposited perpendicular to flow. Some famous air-formed dune A large pile of sediment, deposited perpendicular to flow. As airflow moves sediment along, the grains accumulate on the dune A large pile of sediment, deposited perpendicular to flow.

The angle of the windward side is typically shallower than the leeward downwind side, which has grains falling down over it. This difference in slopes can be seen in a bed A specific layer of rock with identifiable properties. There are typically two styles of dune A large pile of sediment, deposited perpendicular to flow. In tidal locations with strong in-and-out flows, dune A large pile of sediment, deposited perpendicular to flow.

This produces a feature called herringbone cross bedding. Another dune A large pile of sediment, deposited perpendicular to flow. These bed A specific layer of rock with identifiable properties. Antidunes are so named because they share similar characteristics with dune A large pile of sediment, deposited perpendicular to flow. While dune A large pile of sediment, deposited perpendicular to flow. Antidunes form in phase with the flow; in rivers they are marked by rapids in the current.

Antidunes are rarely preserved in the rock record because the high flow rates needed to produce the bed A specific layer of rock with identifiable properties. Bioturbation is the result of organisms burrowing through soft sediment , which disrupts the bedding layers. These tunnels are backfilled and eventually preserved when the sediment becomes rock. Bioturbation happens most commonly in shallow, marine environments, and can be used to indicate water depth.

Mudcracks occur in clay-rich sediment that is submerged underwater and later dries out. When this waterlogged sediment begins to dry out, the clay grains shrink. The sediment layer forms deep polygonal cracks with tapered openings toward the surface, which can be seen in profile.

The cracks fill with new sediment and become visible veins running through the lithified rock. These dried-out clay bed A specific layer of rock with identifiable properties. What makes this sedimentary structure so important to geologists, is they only form in certain depositional environments —such as tidal flats that form underwater and are later exposed to air. Syneresis cracks are similar in appearance to mudcracks but much rarer; they are formed when subaqueous underwater clay sediment shrinks.

Sole marks are small features typically found in river deposits. They form at the base of a bed A specific layer of rock with identifiable properties. They can indicate several things about the deposition conditions, such as flow direction or stratigraphic up-direction see Geopetal Structures section. Flute casts or scour marks are grooves carved out by the forces of fluid flow and sediment loads.

The upstream part of the flow creates steep grooves and downstream the grooves are shallower. The grooves subsequently become filled by overlying sediment , creating a cast Material filling in a cavity left by a organism that has dissolved away.

Formed similarly to flute casts but with a more regular and aligned shape, groove casts are produced by larger clasts or debris carried along in the water that scrape across the sediment layer.

Tool marks come from objects like sticks carried in the fluid downstream or embossed into the sediment layer, leaving a depression that later fills with new sediment.

Load cast Material filling in a cavity left by a organism that has dissolved away. Like their name implies, raindrop impressions are small pits or bumps found in soft sediment. While they are generally believed to be created by rainfall, they may be caused by other agents such as escaping gas bubbles.

Imbrication is a stack of large and usually flat clasts—cobbles, gravels, mud chips , etc. The clasts may be stacked in rows, with their edges dipping down and flat surfaces aligned to face the flow see figure. Or their flat surfaces may be parallel to the layer and long axes aligned with flow.

Imbrications are useful for analyzing paleocurrents , or currents found in the geologic past, especially in alluvial deposits. Geopetal structures , also called up-direction indicators, are used to identify which way was up when the sedimentary rock layers were originally formed. This is especially important in places where the rock layers have been deformed, tilted, or overturned.

Well preserved mudcracks , sole marks , and raindrop impressions can be used to determine up direction. Other useful geopetal structures include:. When mud dries out, mudcracks can form. These only form in conditions where land can be covered by water, then uncovered and dried. Ripples are formed in the slowest flows of the features listed, with speeds right above sediments laid down in flat laminae.

Next fastest are cross bed A specific layer of rock with identifiable properties. Which of these can indicate a paleocurrent and show the direction water has flowed in the past? Asymmetrical ripple marks show a current flowed in the past and indicates the direction it flowed. The ultimate goal of many stratigraphy studies is to understand the original depositional environment. Knowing where and how a particular sedimentary rock was formed can help geologists paint a picture of past environments—such as a mountain glacier , gentle floodplain , dry desert, or deep-sea ocean floor.

The study of depositional environments is a complex endeavor; the table shows a simplified version of what to look for in the rock record. Marine depositional environments are completely and constantly submerged in seawater.

Their depositional characteristics are largely dependent on the depth of water with two notable exceptions, submarine fans and turbidites. Abyssal sedimentary rocks form on the abyssal plain. The plain encompasses relatively flat ocean floor with some minor topographical features, called abyssal hills. These small seafloor mounts range m to 20 km in diameter, and are possibly created by extension.

Most abyssal plains do not experience significant fluid movement, so sedimentary rock formed there are very fine grained. There are three categories of abyssal sediment. Calcareous oozes consist of calcite -rich plankton shells that have fallen to the ocean floor.

An example of this type of sediment is chalk. Siliceous oozes are also made of plankton debris, but these organisms build their shells using silica or hydrated silica. In some cases such as with diatomaceous earth, sediment is deposited below the calcite compensation depth , a depth where calcite solubility increases. Any calcite -based shells are dissolved , leaving only silica-based shells.

Chert is another common rock formed from these types of sediment. These two types of abyssal sediment are also classified as biochemical in origin. The third sediment type is pelagic clay. Very fine-grained clay particles, typically brown or red, descend through the water column very slowly. Pelagic clay deposition occurs in areas of remote open ocean, where there is little plankton accumulation. Two notable exceptions to the fine-grained nature of abyssal sediment are submarine fan and turbidite deposits.

Submarine fans occur offshore at the base of large river systems. They are initiated during times of low sea level, as strong river currents carve submarine canyons into the continental shelf. When sea levels rise, sediment accumulates on the shelf typically forming large, fan-shaped floodplains called deltas. Periodically, the sediment is disturbed creating dense slurries that flush down the underwater canyons in large gravity-induced events called turbidites.

The submarine fan is formed by a network of turbidites that deposit their sediment loads as the slope decreases, much like what happens above-water at alluvial fans and deltas. This sudden flushing transports coarser sediment to the ocean floor where they are otherwise uncommon. Turbidites are also the typical origin of graded Bouma sequences. Continental slope deposits are not common in the rock record.

The most notable type of continental slope deposits are contourites. Contourites form on the slope between the continental shelf and deep ocean floor. Deep-water ocean currents deposit sediment into smooth drifts of various architectures, sometimes interwoven with turbidites. The lower shoreface lies below the normal depth of wave agitation, so the sediment is not subject to daily winnowing and deposition.

These sediment layers are typically finely laminated, and may contain hummocky cross-stratification. Lower shoreface bed A specific layer of rock with identifiable properties. The upper shoreface contains sediments within the zone of normal wave action, but still submerged below the beach environment. These sediments usually consist of very well sorted, fine sand. The main sedimentary structure is planar bedding consistent with the lower part of the upper flow regime , but it can also contain cross bedding created by longshore currents.

Transitional environments, more often called shoreline or coastline environments , are zones of complex interactions caused by ocean water hitting land. The sediment preservation potential is very high in these environments because deposition often occurs on the continental shelf and underwater.

Shoreline environments are an important source of hydrocarbon deposits petroleum , natural gas. The study of shoreline depositional environments is called sequence stratigraphy. Sequence stratigraphy examines depositional changes and 3D architectures associated with rising and falling sea levels, which is the main force at work in shoreline deposits. These sea-level fluctuations come from the daily tides, as well as climate changes and plate tectonics.

A steady rise in sea level relative to the shoreline is called transgression. Regression is the opposite, a relative drop in sea level. Some common components of shoreline environments are littoral zones, tidal flats , reef A topographic high found away from the beach in deeper water, but still on the continental shelf. For a more in-depth look at these environments, see Chapter 12, Coastlines. The littoral zone, better known as the beach, consists of highly weathered, homogeneous, well-sorted sand grains made mostly of quartz.

There are black sand and other types of sand beaches, but they tend to be unique exceptions rather than the rule. Because beach sands, past or present, are so highly evolved, the amount grain weathering can be discerned using the minerals zircon , tourmaline, and rutile. This tool is called the ZTR zircon , tourmaline, rutile index. The ZTR index is higher in more weathered beaches, because these relatively rare and weather -resistant minerals become concentrated in older beaches.

In some beaches, the ZTR index is so high the sand can be harvested as an economically viable source of these minerals. The beach environment has no sedimentary structures, due to the constant bombardment of wave energy delivered by surf action. Beach sediment is moved around via multiple processes. Some beaches with high sediment supplies develop dune A large pile of sediment, deposited perpendicular to flow. Tidal flats , or mud flats , are sedimentary environments that are regularly flooded and drained by ocean tides.

Tidal flats have large areas of fine-grained sediment but may also contain coarser sands. Tidal flat deposits typically contain gradational sediments and may include multi-directional ripple marks. Mudcracks are also commonly seen due to the sediment being regularly exposed to air during low tides; the combination of mudcracks and ripple marks is distinctive to tidal flats.

Tidal water carries in sediment , sometimes focusing the flow through a narrow opening called a tidal inlet. Tidal channels, creek channels influenced by tides, can also focus tidally-induced flow. Areas of higher flow like inlets and tidal channels feature coarser grain sizes and larger ripples , which in some cases can develop into dune A large pile of sediment, deposited perpendicular to flow.

Natural buildups of sand or rock can also create reef A topographic high found away from the beach in deeper water, but still on the continental shelf. Geologically speaking, a reef A topographic high found away from the beach in deeper water, but still on the continental shelf. The term reef A topographic high found away from the beach in deeper water, but still on the continental shelf.

Capitol reef A topographic high found away from the beach in deeper water, but still on the continental shelf. Most reef A topographic high found away from the beach in deeper water, but still on the continental shelf.

The growth habits of coral reef A topographic high found away from the beach in deeper water, but still on the continental shelf.

The hard structures in coral reef A topographic high found away from the beach in deeper water, but still on the continental shelf. Under certain conditions, when the land beneath a reef A topographic high found away from the beach in deeper water, but still on the continental shelf.

Sediment found in coral reef A topographic high found away from the beach in deeper water, but still on the continental shelf. Water with high levels of silt or clay particles can inhibit the reef A topographic high found away from the beach in deeper water, but still on the continental shelf. Inorganic reef A topographic high found away from the beach in deeper water, but still on the continental shelf. Examples include the Emperor Seamounts , formed millions of years ago over the Hawaiian Hotspot.

If the reef A topographic high found away from the beach in deeper water, but still on the continental shelf. Lagoons are small bodies of seawater located inland from the shore or isolated by another geographic feature, such as a reef A topographic high found away from the beach in deeper water, but still on the continental shelf. Because they are protected from the action of tides, currents, and waves, lagoon environments typically have very fine grained sediments. Lagoons , as well as estuaries , are ecosystems with high biological productivity.

Rocks from these environments often includes bioturbation marks or coal Former swamp-derived plant material that is part of the rock record. Around lagoons where evaporation exceeds water inflow, salt flats, also known as sabkhas, and sand dune A large pile of sediment, deposited perpendicular to flow.

This is most often seen in marine settings. Deltas form where rivers enter lakes or oceans and are of three basic shapes: river -dominated deltas, wave-dominated deltas, and tide Movements of water rising and falling due to the gravity of the moon and sun. The name delta Place where rivers enter a large body of water, forming a triangular shape as the river deposits sediment and switches course. The velocity of water flow is dependent on riverbed slope or gradient , which becomes shallower as the river descends from the mountains.

The flow velocity quickly drops as well, and sediment is deposited, from coarse clasts, to fine sand, and mud to form the delta Place where rivers enter a large body of water, forming a triangular shape as the river deposits sediment and switches course.

As one part of the delta Place where rivers enter a large body of water, forming a triangular shape as the river deposits sediment and switches course. Deltas are organized by the dominant process that controls their shape: tide Movements of water rising and falling due to the gravity of the moon and sun.

Wave-dominated deltas generally have smooth coastlines and beach-ridges on the land that represent previous shorelines. The Nile River delta Place where rivers enter a large body of water, forming a triangular shape as the river deposits sediment and switches course. The Mississippi River delta Place where rivers enter a large body of water, forming a triangular shape as the river deposits sediment and switches course.

Other times the tides or the waves can be a bigger factor, and can reshape the delta Place where rivers enter a large body of water, forming a triangular shape as the river deposits sediment and switches course. A tide Movements of water rising and falling due to the gravity of the moon and sun. During flood stages when rivers have lots of water available, it develops distributaries that are separated by sand bars and sand ridges.

The tidal delta Place where rivers enter a large body of water, forming a triangular shape as the river deposits sediment and switches course. Terrestrial depositional environments are diverse. Water is a major factor in these environments, in liquid or frozen states, or even when it is lacking arid conditions.