what is hypothesis of mass movement

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mass movement

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• The Idaho Museum of Natural History - Digital Atlas of Idaho - What is Mass Movement?

mass movement , bulk movements of soil and rock debris down slopes in response to the pull of gravity , or the rapid or gradual sinking of the Earth’s ground surface in a predominantly vertical direction. Formerly, the term mass wasting referred to a variety of processes by which large masses of crustal materials are moved by gravity from one place to another. More recently, the term mass movement has been substituted to include mass wasting processes and the sinking of confined areas of the Earth’s ground surface. Mass movements on slopes and sinking mass movements are often aided by water and the significance of both types is the part each plays in the alteration of landforms.

The variety of downslope mass movements reflects the diversity of factors that are responsible for their origin. Such factors include: weathering or erosional debris cover on slopes, which is usually liable to mass movement; the character and structure of rocks, such as resistant permeable beds prone to sliding because of underlying impermeable rocks; the removal of the vegetation cover, which increases the slope’s susceptibility to mass movement by reducing its stability; artificial or natural increases in the slope’s steepness, which will usually induce mass movement; earthquake tremors, which affect the slope equilibrium and increase the likelihood of mass movement; and flowing ground water, which exerts pressure on soil particles and impairs slope stability. These factors affecting slope conditions will often combine with climatic factors such as precipitation and frost activity to produce downslope mass movement.

The types of mass movements caused by the above factors include: the abrupt movement and free fall of loosened blocks of solid rock , known as rockfalls; several types of almost imperceptible downslope movement of surficial soil particles and rock debris, collectively called creep; the subsurface creep of rock material, known as bulging: the multiplicity of downslope movements of bedrock and other debris caused by the separation of a slope section along a plane of least resistance or slip surface, collectively called landslides; the separation of a mass along a concave head scarp, moving down a curved slip surface and accumulating at the slope’s foot, known as a slump; the saturation of debris and weathered material by rainfall in the upper section of a slope or valley, increasing the weight of the debris and causing a slow downslope movement, called an earthflow; a rapidly moving earthflow possessing a higher water content, known as a mudflow; a fast-moving earthflow in a mountainous region, called a debris flow or avalanche; and the downslope movement of moisture-saturated surficial material, known as solifluction , over frozen substratum material, occurring in sub-Arctic regions during seasonal periods of surface thaw.

Sinking mass movements occur in relatively rapid fashion, known as subsidence , and in a gradual manner, called settlement . Subsidence involves a roof collapse or breakdown of a subsurface cavity such as a cave. Extensive subsidence is evident in areas where coal, salt, and metalliferous ores are mined. Marine erosion sometimes causes the roof collapse of sea caves. Regions of karst topography will exhibit widespread subsidence in the form of sinkholes caused by underground drainage. Other types of subsidence caused by underground solutions have been found in chalk, gypsum, anhydrite, halite (salt), and loess terrains. The melting of ground ice also contributes to subsidence such as the formation of glacial kettles and depressions following the seasonal surface thaw of perennially frozen land. The chemical decomposition of subsurface rocks and ores is also a cause of subsidence. Another form of subsidence is the steep-walled depression, known as a volcanic sink, formed following the withdrawal of magma from below the ground surface.

The gradual settlement of confined areas of earth material occurs through consolidation of soil and rock by the squeezing or removal of fluids from the pore spaces, and by the collapse of the grain structure. The most widespread cause of consolidation is by surface loading such as the continued deposition of sediments in sea and lake beds or by loads imposed on land by glacial ice sheets or outwash deposits. Human-made structures also cause surface loading, consolidation, and settlement. Consolidation is also caused by the lowering of the ground water table . The extraction of pressurized water or oil from deep beneath the surface will cause a collapse of the pore spaces and consolidation of rock material. Grain structure collapse usually occurs from the wetting of rock materials such as clays and sands, which causes the structure of the grains to shift and settle in a more compact and dense configuration.

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What is mass movement?

The movement of cliff material caused by erosion , weathering and gravity.

What is Mass Movement?

Mass movement is the downhill movement of cliff material under the influence of gravity. There are a range of different types of mass movement. These are explored below.

Types of mass movement

Slumping / Rotational Slip

Cliffs formed from boulder clay , material deposited by glacial periods, are susceptible to high rates of coastal erosion . The Holderness Coast is an example of a coastline formed from boulder clay and is the fastest-eroding coastline in Europe. The soft boulder clay is quickly eroded through hydraulic action and abrasion . However, this is not the only way it is being eroded. Sub-aerial processes, such as rainfall, also cause erosion. This often happens when layers of boulder clay, left behind by melting glaciers, become saturated and cause the cliff to slump. The debris on the beach is then eroded by the sea, leaving the cliff exposed once more. 

An annotated diagram showing the main features of slumping.

Slumping explained:

Stage 1 – the soft boulder clay holds rainwater and run-off.

Slumping stage 1

Stage 2 – Waves erode the base of the cliff creating a wave-cut notch. The clay becomes saturated and forms a slip plane.

Slumping stage 2

Stage 3 – The weight of the saturated cliff causes it to slump.

Slumping stage 3

The video below shows evidence of slumping at Mappleton, Holderness Coast. The video shows the early stages of the process. Water will percolate down the large crack to lubricate the slip plane. This will cause the cliff to slump further down.

In areas of more resistant cliff material erosion is greatest when waves break at the foot of a cliff. This causes erosion at the base of the cliff. This creates a wave-cut notch in the base of the cliff. As the notch increases in size, the weight of the cliffs above becomes too much to support, leading to a landslide. This material will provide temporary protection for the cliff behind. However, once the sea has removed it, this process will occur again. Wave-cut platforms will be created where cliffs are made of more resistant material.

An annotated diagram showing the main features of a landslide.

The image below shows a landslide at West Bay , Dorset.

Landslide at West Bay on Dorset’s Jurassic Coast.

The video below shows evidence of a landslide at Port Mulgrave, Yorkshire and Cleveland Heritage Coast.

A rockfall involves rock fragments breaking away from the cliff face, often due to freeze-thaw weathering.

An annotated diagram showing the main features of a rock fall.

The video below shows a series of rock falls above a landslide at Port Mulgrave, Yorkshire.

Mudslides occur when saturated soil and weak rock flow down a slope. These typically occur where cliffs are made up of boulder clay.

An annotated diagram showing the main features of a mudslide.

The image below shows a mudslide at Mappleton, Holderness Coast.

A mudslide at Mappleton

The video below shows evidence of a mudslide at Mappleton.

The video below shows evidence of a small mudflow at Hornsea, Holderness Coast.

You can view more videos on the mass movement video page .

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82 Mass Movement: Landslides

Mass movement can be devastating and costly. Landslides and avalanches may not be something we really think about unless we live in an area prone to them, but mass wasting can occur just about anywhere.

The Science of Mudslides | How It Happens | :

Earthflow in Italy in 2010:

Mass wasting can be very fast or slow. What do you make of the photo below?

Do you notice anything strange about the trees? Would you want to live in an area like this?

Most recent in US: WA, Oso, March 22, 2014

http://www.nytimes.com/interactive/2014/03/26/us/houses-in-the-path-of-the-washington-mudslide.html?_r=0

Before landslide

After landslide

Bingham Canyon (copper mining operation), April 10, 2013

On the evening of 10 April 2013 (MDT) a massive landslide occurred at the Bingham Canyon copper mine near Salt Lake City, Utah, USA. The northeastern wall of the 970-m-deep pit collapsed in two distinct episodes that were each sudden, lasting ~90 seconds, but separated in time by ~1.5 hours. In total, ~65 million cubic meters of material was deposited, making the cumulative event likely the largest non-volcanic landslide to have occurred in North America in modern times. Fortunately, there were no fatalities or injuries. Because of extensive geotechnical surveillance, mine operators were aware of the instability and had previously evacuated the area.

    Resettlement Option discussion (2018) ;  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6100022/

Geology 101 for Lehman College (CUNY) Copyright © by Yuri Gorokhovich and Lumen Learning is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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A mass movement classification for the southern Drakensberg, South Africa

Journal title, journal issn, volume title, description, collections.

The Mass Flow Hypothesis ( AQA A Level Biology )

Revision note.

Biology Lead

Phloem: Mass Flow

• The Mass Flow Hypothesis was the model initially used to explain the movement of assimilates in the phloem tissue
• Two partially permeable membranes containing solutions with different concentrations of ions (one dilute the other concentrated)
• These two membranes were placed into two chambers containing water and were connected via a passageway
• The two membranes were joined via a tube
• As the membranes were surrounded by water, the water moved by osmosis across the membrane containing the more concentrated solution which forced the solution towards the membrane containing the more dilute solution (where water was being forced out of due to hydrostatic pressure)
• Scientists now support a modified version of this hypothesis – the pressure flow gradient

An illustration of Münch’s model for mass flow in phloem tissue

Pressure (hydrostatic) flow gradient

• Phloem sap (containing sucrose and other organic solutes) moves by mass flow up and down the plant
• It allows for efficient energy transfer and increased energy storage (sucrose is a disaccharide and therefore contains more energy)
• It is less reactive than glucose as it is a non-reducing sugar and therefore no intermediate reactions occur as it is being transported
• The advantage of mass flow is that it moves the organic solutes faster than diffusion
• In xylem tissue the pressure difference that causes mass flow occurs because of a water potential gradient between the soil and leaf (this requires no energy input by the plant)
• However in phloem tissue energy is required to create pressure differences for the mass flow of the organic solutes
• The pressure difference is generated by actively loading sucrose into the sieve elements at the source (usually a photosynthesising leaf or storage organ) which lowers the water potential in the sap
• This results in water moving into the sieve elements as it travels down the water potential gradient by osmosis
• The presence of water within the sieve elements increases the hydrostatic or turgor pressure at the source and as solutes (eg. sucrose) are removed / unloaded from the sieve elements causing water to follow by osmosis at the sink (creating a low hydrostatic pressure ), a hydrostatic pressure gradient occurs
• The pressure difference between the source and the sink results in the mass flow of water (containing the dissolved organic solutes) from the high hydrostatic pressure area to the low hydrostatic pressure area
• The mass flow of organic solutes within the phloem tissue occurs above and below the sources (which is typically photosynthesising leaves). Therefore sap flows upwards and downwards within a plant

The translocation of phloem sap (sucrose and other organic solutes) due to a hydrostatic pressure gradient from the source to the sink

Remember that the source is not necessarily the leaves and the sink is not necessarily the roots. Phloem sap moves up and down the plant (although it will only move in one direction per sieve tube). The hydrostatic pressure gradient is dependent on water moving in and out of the xylem vessels by osmosis.

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• Biology Article

Mass Flow Hypothesis

Table of Contents

Introduction

The Mass Flow Hypothesis was first proposed by German plant physiologist Ernst Munch in the year 1930. He theorised the movement of sap through the phloem tissue in plants. This theory is also known as the Pressure Flow Hypothesis. A highly concentrated organic sugar especially sugar in the cells of the phloem from a source like a leaf forms a diffusion gradient which draws water into the cells of phloem tissue from the adjacent xylem. This develops turgor pressure in the phloem, which is also called hydrostatic pressure.

Phloem movement occurs by mass flow from sources of sugar to sugar sinks. The phloem movement is bidirectional but unidirectional in xylem cells. Due to this multidirectional flow, it is not uncommon for sap in the sieve tubes besides to move in opposite directions based on the fact that sap cannot travel easily between adjacent sieve tubes.

When the movement of minerals and water via the xylem is driven mostly by negative pressure and movement via phloem is driven by hydrostatic pressure. This process is called translocation and is accompanied by a process known as phloem loading and unloading. Cells in sugar sources load a sieve tube by osmosis developing pressure that pushes the sap low. The cells deliver solutes out of the elements of sieve tube and produce opposite effects. The sugar gradient from the source creates pressure-flow via the sieve tube towards the sink.

• Glucose is formed by photosynthesis in the cells of mesophyll and some glucose is utilized in the cells during respiration. The leftover glucose is transformed into non-reducing sugar.
• Sucrose is delivered to the neighbour cells of minute veins of the leaves.
• Sucrose diffuses from neighbour cells to the elements of the sieve tube via plasmodesmata. Hence, the amount of sucrose rises in the elements of the sieve tube.
• Water travels from the close xylem to the leaf vein by osmosis and raises the hydrostatic pressure of the elements of the sieve tube.
• The Hydrostatic pressure shifts the sucrose along with other substances via the cell of the sieve tube towards the sink.
• In storage sinks, sucrose is eliminated into the apoplast before entering the sink’s symplast.
• The water travels out of the cells via osmosis and lowers the hydrostatic pressure in them. Hence, a gradient of pressure is developed as a result of the entry of sugar at the source and elimination of sucrose at the sink.
• The phloem sugar is eradicated by the cortex of the root and stem and utilized by cellular respiration. The starch is insoluble and does not exert any osmotic effect. Ultimately, pure water is left and drawn into xylem vessels by transpiration pull.

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Mass Movement

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Dechano, L.M. (2007). Mass Movement. In: Lidstone, J., Dechano, L.M., Stoltman, J.P. (eds) International Perspectives on Natural Disasters: Occurrence, Mitigation, and Consequences. Advances in Natural and Technological Hazards Research, vol 21. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-2851-9_6

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Mass Flow Hypothesis: Theory, Mechanism, and Criticism

Jasmine Grover

Senior Content Specialist

Mass flow hypothesis, also known as pressure-flow hypothesis, is an important theory of biology. It is mainly concerned with explanation of the movement of sap via phloem in a plant. The theory was proposed in 1930 by Ernst Munch. A highly concentrated sugar, especially the one present in the cells of phloem, form a diffusion gradient that is responsible for eventually drawing water in adjacent xylem cells. In this article, we will read about mass flow hypothesis, its origin, mechanism, and various other corresponding topics.

Key Takeaways : Mass flow, phloem, xylem, sucrose, organic sugar, pressure gradient, hydrostatic pressure, bilateral movement

What is Mass Flow Hypothesis?

Mass flow hypothesis or pressure-flow hypothesis is a theory that originated in 1930. It was a German plant physiologist, named Ernst Munch, who worked upon it to explain the concept of movement or transportation  of sap through phloem in a plant.

This hypothesis explains that the presence of highly concentrated and organic sugar in the cell of phloem of plant is the main reason behind the flow of water within it. This sugar tends to draw water from xylem and in turn, develops the hydrostatic pressure also known as turgor pressure in the phloem. Therefore, bi-directional movement in the phloem takes place due to mass flow from sugar to the sugar sinks. However, this movement is unidirectional in the cells of  xylem.

Mass Flow Hypothesis Mechanism

The mechanism of mass flow is driven by multiple concepts. Let us have a look at some of them:

• Beginning with process of translocation , which states about the negative pressure which is mainly responsible for movement of minerals and water via xylem and hydrostatic pressure which is, on the other hand, responsible for the movement via phloem.
• This process of translocation is often accompanied by another process, namely, phloem loading and unloading . In this process, sugar sources are mainly used which undergo osmosis in order to load a sieve tube. This, in turn, develops pressure that pushes the sap low. The further working of movement of the sap is maintained by pressure gradient managed by the leaf.
• Photosynthesis leads to the formation of glucose in mesophyll. Some amount of glucose is utilized in respiration.
• Whereas, the remaining amount of glucose is transformed into a type of non-reducing sugar.
• This even forms sucrose which is used by cells of the leaves consisting of minute veins.
• This sucrose along with other substances is further moved towards the sink through cell of the sieve tube. All this happens due to the existing Hydrostatic pressure.
• However, from the sinks, sucrose is further eliminated into  apoplast.
• On the other hand, water reaches the leaf through xylem while undergoing the process of osmosis .
• Now, when osmosis occurs, water moves out of the cell, lowering hydrostatic pressure and developing a pressure gradient.
• Sugar present in phloem shall be utilized by cellular respiration after being eradicated by the cortex of  root and stem, as per mass flow hypothesis.

Read More: Life Processes

Criticism of Mass Flow Hypothesis

There is a lot of criticism related to mass flow hypothesis theory. Some of them are:

• Many critics believed that process of translocation happens due to metabolic process and not due to hydrostatic pressure.
• As the hypothesis talks about the uniform rate of transmission of material inside phloem and sieve tube, critics have disagreed with the same.
• Critics also argued that the reason behind bilateral movement of the material has not been explained wisely.

Things to Remember

• Mass flow hypothesis involves great experiments and facts and was propounded by Ernst Munch. 
• This great theory was manifested in his book where he simply dedicated 230 pages only to the fluid circulation within plants.
• However, even after propounding something so novel, Munch never realized that it was original and new.
• As per mass flow hypothesis, Sucrose has the tendency of getting diffused into sieve tube from neighbor cells.
• This entire process of diffusion of sucrose takes place through plasmodesmata . Thus, raising the amount of sucrose in elements of sieve tube.
• When the elimination of sucrose takes place in storage sinks, it shall always occur before sucrose enters symplast of the sink.

Check out:   Energy Currency of the Cell

Sample Questions

Ques. Who found mass flow hypothesis? (3 marks)

Ans. Mass flow hypothesis or pressure-flow hypothesis is a theory that originated in 1930. It was a German plant physiologist, named Ernst Munch, who worked upon it to explain the concept of movement of sap through phloem in a plant. This hypothesis explains that the presence of highly concentrated and organic sugar in the cell of phloem of  plant is the main reason behind flow of water within it.

This sugar tends to draw water fromxylem and in turn, develops hydrostatic pressure also known as turgor pressure in phloem. Therefore, the bi-directional movement in phloem takes place due to mass flow from sugar to the sugar sinks. However, this movement is unidirectional in the cells of the xylem.

Ques. What is the main idea behind mass flow hypothesis? (5 marks)

Ans. This hypothesis explains that the presence of highly concentrated and organic sugar in the cell of phloem of the plant is the main reason behind flow of water within it. This sugar tends to draw water from xylem and in turn, develops hydrostatic pressure also known as turgor pressure in phloem. Therefore, the bi-directional movement in phloem takes place due to the mass flow from sugar to the sugar sinks. However, this movement is unidirectional in the cells of xylem.

Ques. Explain three criticisms of mass flow hypothesis.  (3 marks)

Ans. The three criticisms are as follows.

• As the hypothesis talks about uniform rate of transmission of material inside phloem and sieve tube, the critiques have disagreed with the same.
• Critiques also argued that the reason behind bilateral movement of the material has not been explained wisely.

Ques. Explain the process of translocation in context of mass flow hypothesis.  (2 marks)

Ans. Process of translocation states about the negative pressure which is mainly responsible for the movement of minerals and water via xylem and hydrostatic pressure which is, on the other hand, responsible for the movement via phloem. This process of translocation is often accompanied by another process, namely, phloem loading and unloading . In this process, sugar sources are mainly used which undergo osmosis in order to load a sieve tube. This, in turn, develops pressure that pushes the sap low. The further working of movement of the sap is maintained by pressure gradient managed by the leaf.

Ques. Explain the mechanism of mass flow hypothesis in brief.  (5 marks)

Ans. The mechanism of mass flow hypothesis is as follows.

• Beginning with  process of translocation , which states about negative pressure which is mainly responsible for the movement of minerals and water via xylem and hydrostatic pressure which is, on the other hand, responsible for the movement via phloem.
• This process of translocation is often accompanied by another process, namely, phloem loading and unloading . In this process, sugar sources are mainly used which undergo osmosis in order to load a sieve tube. Photosynthesis leads to the formation of glucose in mesophyll. Some amount of glucose is utilized in respiration.
• Whereas, remaining amount of glucose is transformed into the type of non – reducing sugar.
• This even forms sucrose which is used by the cells of leaves consisting of the minute veins.
• This sucrose along with other substances is further moved towards the sink through the cell of sieve tube. All this happens due to the existing Hydrostatic pressure.
• However, from the sinks, the sucrose is further eliminated into the apoplast.
• On the other hand, water reaches the leaf through xylem while undergoing the process of osmosis.
• Now, when osmosis occurs, the water moves out of the cell lowering hydrostatic pressure and developing a pressure gradient.
• The sugar present in phloem shall be utilized by cellular respiration after being eradicated by the cortex of root and stem, as per mass flow hypothesis.

Ques. How has Munch used pressure gradient and hydrostatic pressure in his mass flow hypothesis? (3 marks)

Ans. Mass flow hypothesis explains that the presence of highly concentrated and organic sugar in the cell of phloem of plant is the main reason behind the flow of water within it. This sugar tends to draw water from xylem and in turn, develops the hydrostatic pressure also known as turgor pressure in the phloem. Therefore, the bi-directional movement in the phloem takes place due to the mass flow from sugar to the sugar sinks. However, this movement is unidirectional in the cells of  xylem.

The hypothesis involves process of translocation, which states about the negative pressure which is mainly responsible for the movement of minerals and water via xylem, and  hydrostatic pressure which is, on the other hand, responsible for the movement via phloem.

This process of translocation is often accompanied by another process, namely, phloem loading and unloading. In this process, sugar sources are mainly used which undergo osmosis in order to load a sieve tube. This, in turn, develops pressure that pushes the sap low. The further working of movement of sap is maintained by the pressure gradient managed by leaf.

Ques. What is the process of phloem loading and unloading?  (2 marks)

Ans. The process of phloem loading and unloading is followed by the process of translocation, according to mass flow hypothesis. In this process, sugar sources are mainly used which undergo osmosis in order to load a sieve tube. This, in turn, develops pressure that pushes the sap low. The further working of movement of the sap is maintained by the pressure gradient managed by leaf.

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