10 Mass Wasting
Learning Objectives
By the end of this chapter, students should be able to:
- Explain what is and why it occurs on a slope.
- Explain the basic triggers of mass-wasting events and how they occur.
- Identify types of .
- Identify risk factors for mass-wasting events.
- Evaluate and their contributing factors.
This chapter discusses the fundamental processes driving mass-wasting, types of , examples and lessons learned from famous mass-wasting events, how can be predicted, and how people can be protected from this potential hazard. is the downhill movement of rock and material due to gravity. The term is often used as a synonym for , but is a much broader term referring to all movement downslope. Geologically, is a general term for that involves fast-moving geologic material. Loose material along with overlying are what typically move during a mass-wasting event. Moving blocks of are called rock topples, rock slides, or rock , depending on the dominant motion of the blocks. Movements of dominantly liquid material are called flows. Movement by can be slow or rapid. Rapid movement can be dangerous, such as during . Areas with steep topography and rapid rainfall, such as the California coast, Rocky Mountain Region, and Pacific Northwest, are particularly susceptible to hazardous mass-wasting events.
10.1 Slope Strength

occurs when a slope fails. A slope fails when it is too steep and unstable for existing materials and conditions. Slope stability is ultimately determined by two principal factors: the slope angle and the strength of the underlying material. Force of gravity, which plays a part in , is constant on the Earth’s surface for the most part, although small variations exist depending on the elevation and density of the underlying rock. In the figure, a block of rock situated on a slope is pulled down toward the Earth’s center by the force of gravity (fg). The gravitational force acting on a slope can be divided into two components: the or (fs) pushing the block down the slope, and the normal or (fn) pushing into the slope, which produces friction. The relationship between and is called . When the normal force, i.e., friction, is greater than the , then the block does not move downslope. However, if the slope angle becomes steeper or if the earth material is weakened, exceeds , compromising , and downslope movement occurs.

In the figure, the force vectors change as the slope angle increases. The gravitational force doesn’t change, but the increases while the decreases. The steepest angle at which rock and material is stable and will not move downslope is called the . The is measured relative from the horizontal. When a slope is at the , the is in equilibrium with the . If the slope becomes just slightly steeper, the exceeds the , and the material starts to move downhill. The varies for all material and slopes depending on many factors such as , grain , and water content. The figure shows the for sand that is poured into a pile on a flat surface. The sand grains cascade down the sides of the pile until coming to rest at the . At that angle, the base and height of the pile continue to increase, but the angle of the sides remains the same.

Water is a common factor that can significantly change the of a particular slope. Water is located in spaces, which are empty air spaces in or rocks between the grains. For example, assume a dry sand pile has an of 30 degrees. If water is added to the sand, the will increase, possibly to 60 degrees or even 90 degrees, such as a sandcastle being built at a beach. But if too much water is added to the pore spaces of the sandcastle, the water decreases the , lowers the , and the sandcastle collapses.
Another factor influencing are planes of weakness in sedimentary rocks. planes (see chapter 5) can act as significant planes of weakness when they are parallel to the slope but less so if they are perpendicular to the slope. At locations A and B, the is nearly perpendicular to the slope and relatively stable. At location D, the is nearly parallel to the slope and quite unstable. At location C, the is nearly horizontal, and the stability is between the other two extremes. Additionally, if clay form along planes, they can absorb water and become slick. When a plane of (clay and silt) becomes , it can lower the of the rock mass and cause a , such as at the 1925 Gros Ventre, Wyoming rock slide. See the case studies section for details on this and other .

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10.2 Mass-Wasting Triggers & Mitigation
Mass-wasting events often have a : something changes that causes a to occur at a specific time. It could be rapid snowmelt, intense rainfall, earthquake shaking, eruption, storm waves, rapid-stream , or human activities, such as a new road. Increased water content within the slope is the most common mass-wasting . Water content can increase due to rapidly melting snow or ice or an intense rain event. Intense rain events can occur more often during El Niño years. Then, the west coast of North America receives more than normal, and become more common. Changes in surface-water conditions resulting from earthquakes, previous slope failures that dam up , or human structures that interfere with , such as buildings, roads, or parking lots can provide additional water to a slope. In the case of the 1959 Hebgen Lake rock slide, Madison Canyon, Montana, the of the slope may have been weakened by earthquake shaking. Most mitigation diverts and drains water away from slide areas. Tarps and plastic sheeting are often used to drain water off of slide bodies and prevent into the slide. Drains are used to dewater and shallow wells are used to monitor the water content of some active .
An slope may also . Slopes can be made excessively steep by natural processes of or when humans modify the landscape for building construction. An example of how a slope may be during development occurs where the bottom of the slope is cut into, perhaps to build a road or level a building lot, and the top of the slope is modified by depositing excavated material from below. If done carefully, this practice can be very useful in land development, but in some cases, this can result in devastating consequences. For example, this might have been a contributing factor in the 2014 North Salt Lake City, Utah . A former gravel pit was regraded to provide a road and several building lots. These activities may have the slope, which resulted in a slow moving that destroyed one home at the bottom of the slope. Natural processes such as excessive from a flood or coastal erosion during a storm can also slopes. For example, natural undercutting of the riverbank was proposed as part of the for the famous 1925 Gros Ventre, Wyoming rock slide.
Slope reinforcement can help prevent and mitigate . For -prone areas, sometimes it is economical to use long steel bolts. Bolts, drilled a few meters into a rock face, can secure loose pieces of material that could pose a hazard. Shockcrete, a reinforced spray-on form of concrete, can strengthen a slope face when applied properly. Buttressing a slide by adding weight at the toe of the slide and removing weight from the head of the slide, can stabilize a . Terracing, which creates a stairstep topography, can be applied to help with slope stabilization, but it must be applied at the proper scale to be effective.
A different approach in reducing hazard is to , catch, and divert the runout material. Sometimes the most economical way to deal with a hazard is to divert and slow the falling material. Special stretchable fencing can be applied in areas where is common to protect pedestrians and vehicles. Runout channels, diversion structures, and check dams can be used to slow and divert them around structures. Some highways have special tunnels that divert over the highway. In all of these cases the shielding has to be engineered to a scale that is greater than the slide, or catastrophic loss in property and life could result.
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10.3 Landslide Classification & Identification
Mass-wasting events are classified by type of movement and type of material, and there are several ways to classify these events. The figure and table show terms used. In addition, mass-wasting types often share common morphological features observed on the surface, such as the head scarp—commonly seen as crescent shapes on a cliff face; hummocky or uneven surfaces; accumulations of —loose rocky material falling from above; and toe of slope, which covers existing surface material.
10.3.1 Types of Mass Wasting
The most common mass-wasting types are , rotational and , flows, and . are abrupt rock movements that detach from steep slopes or cliffs. Rocks separate along existing natural breaks such as or planes. Movement occurs as free-falling, bouncing, and rolling. are strongly influenced by gravity, , and water. commonly show slow movement along a curved rupture surface. often are rapid movements along a plane of distinct weakness between the overlying slide material and more stable underlying material. Slides can be further subdivided into rock slides, debris slides, or earth slides depending on the type of the material involved (see table).
Type of movement | Primary material type and common name of slide | ||
---|---|---|---|
Bedrock | Soil: mostly coarse-grained | Soil: mostly fine-grained | |
Falls | Rock fall | ||
Rock avalanche | Rock avalanche | ||
Rotational slide (slump) | Rotational debris slide (slump) | Rotational Earth slide (slump) | |
Transitional slide | Transitional rock slide | Transitional debris slide | Transitional Earth slide |
Flows | Debris flow | Earth flow | |
Soil creep | Creep | Creep |
Table 10.1: Mass wasting types.

Flows are rapidly moving mass-wasting events in which the loose material is typically mixed with abundant water, creating long runouts at the slope base. Flows are commonly separated into (coarse material) and (fine material) depending on the type of material involved and the amount of water. Some of the largest and fastest flows on land are called , or long runout . They are still poorly understood, but are known to travel for long distances, even in places without significant atmospheres like the Moon.
is the imperceptibly slow downward movement of material caused by a regular cycle of nighttime freezing followed by daytime thawing in unconsolidated material such as . During the freeze, expansion of ice pushes particles out away from the slope, while the next day following the thaw, gravity pulls them directly downward. The net effect is a gradual movement of surface particles downhill. is indicated by curved tree trunks, bent fences or retaining walls, tilted poles or fences, and small or ridges. A special type of is solifluction, which is the slow movement of lobes on low-angle slopes due to seasonally freezing and thawing in high-, typically sub-Arctic, Arctic, and Antarctic locations.
Video 10.1: Landslide hazards.
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10.3.2 Parts of a Landslide
have several identifying features that can be common across the different types of . Note that there are many exceptions, and a does not have to have these features. Displacement of material by causes the absence of material uphill and the of new material downhill, and careful can identify the evidence of that displacement. Other signs of include tilted or structures or natural features that would normally be vertical or in place.
Many have escarpments or scarps. scarps, like , are steep terrain created when movement of the adjacent land exposes a part of the subsurface. The most prominent scarp is the main scarp, which marks the uphill extent of the . As the disturbed material moves out of place, a step slope forms and develops a new hillside escarpment for the undisturbed material. Main scarps are formed by movement of the displaced material away from the undisturbed ground and are the visible part of slide rupture surface.
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The slide rupture surface is the boundary of the body of movement of the . The geologic material below the slide surface does not move, and is marked on the sides by the flanks of the and at the end by the toe of the .
The toe of the marks the end of the moving material. The toe marks the runout, or maximum distance traveled, of the . In rotational , the toe is often a large, disturbed mound of geologic material, forming as the moves past its original rupture surface.
Rotational and translational often have cracks, sag ponds, hummocky terrain and pressure ridges. cracks form when a ’s toe moves forward faster than the rest of , resulting in forces. Sag ponds are small bodies of water filling depressions formed where movement has impounded . Hummocky terrain is undulating and uneven topography that results from the ground being disturbed. Pressure ridges develop on the margins of the where material is forced upward into a ridge structure.
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10.4 Examples of Landslides
10.4.1 Landslides in United States

Gros Ventre, Wyoming (1925): On June 23, 1925, a 38 million cubic meter (50 million cu yd) translational rock slide occurred next to the Gros Ventre River (pronounced “grow vont”) near Jackson Hole, Wyoming. Large boulders dammed the Gros Ventre River and ran up the opposite side of the valley several hundred vertical feet. The dammed created Slide Lake, and two years later in 1927, lake levels rose high enough to destabilize the dam. The dam failed and caused a catastrophic flood that killed six people in the small downstream community of Kelly, Wyoming.

A combination of three factors caused the rock slide: 1) heavy rains and rapidly melting snow the Tensleep sandstone causing the underlying of the Amsden Formation to lose its , 2) the Gros Ventre River cut through the creating an slope, and 3) soil on top of the mountain became saturated with water due to poor . The cross-section diagram shows how the parallel planes between the Tensleep sandstone and Amsden Formation offered little friction against the slope surface as the undercut the . Lastly, the rockslide may have been triggered by an earthquake.
Madison Canyon, Montana (1959): In 1959, the largest earthquake in Rocky Mountain recorded history, 7.5, struck the Hebgen Lake, Montana area, causing a destructive seiche on the lake (see chapter 9). The earthquake caused a rock avalanche that dammed the Madison River, creating Quake Lake, and ran up the other side of the valley hundreds of vertical feet. Today, there are still house-sized boulders visible on the slope opposite their starting point. The slide moved at a velocity of up to 160.9 kph (100 mph), creating an incredible air blast that swept through the Rock Creek Campground. The slide killed 28 people, most of whom were in the campground and remain buried there. In a manner like the Gros Ventre slide, planes of weakness in outcrops were parallel with the surface, compromising .

Mount Saint Helens, Washington (1980): On May 18, 1980 a 5.1- earthquake triggered the largest observed in the historical record. This was followed by the lateral eruption of Mount Saint Helens , and the eruption was followed by known as . The volume of material moved by the was 2.8 cubic kilometers (0.67 mi3).
La Conchita, California (1995 and 2005): On March 4, 1995, a fast-moving damaged nine houses in the southern California coastal community of La Conchita. A week later, a in the same location damaged five more houses. Surface- cracks at the top of the slide gave early warning signs in the summer of 1994. During the rainy winter season of 1994/1995, the cracks grew larger. The likely of the 1995 event was unusually heavy rainfall during the winter of 1994/1995 and rising levels. Ten years later, in 2005, a rapid- occurred at the end of a 15-day of near-record rainfall in southern California. Vegetation remained relatively intact as it was rafted on the surface of the rapid flow, indicating that much of the mass simply was being carried on a presumably much more and fluidized layer beneath. The 2005 slide damaged 36 houses and killed 10 people.



Oso Landslide, Washington (2014): On March 22, 2014, a of approximately 18 million tons (10 million yd3) traveled at 64 kph (40 mph), extended for nearly a 1.6 km (1 m), and dammed the North Fork of the Stillaguamish River. The covered 40 homes and killed 43 people in the Steelhead Haven community near Oso, Washington. It produced a volume of material equivalent to 600 football fields covered in material 3 m (10 ft) deep. The winter of 2013-2014 was unusually wet with almost double the average amount of . The occurred in an area of the Stillaguamish River Valley historically active with many , but previous events had been small.

Yosemite National Park Rock Falls: The steep cliffs of Yosemite National Park cause frequent rock . created to and and expanded by can cause house-sized blocks of to detach from the cliff-faces of Yosemite National Park. The park models potential runout, the distance material travels, to better assess the risk posed to the millions of park visitors.
Video 10.2: Rock fall in Yosemite.
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10.4.2 Landslides in Utah

Markagunt Gravity Slide: About 21–22 million years ago, one of the biggest land-based yet discovered in the geologic record displaced more than 1,700 cu km (408 cu mi) of material in one relatively fast event. Evidence for this slide includes breccia (see chapter 5), glassy pseudotachylytes, (see chapter 6), slip surfaces (similar to ) see chapter 9), and (see chapter 7). The is estimated to encompass an area the size of Rhode Island and to extend from near Cedar City, Utah to Panguitch, Utah. This was likely the result of material released from the side of a growing (a type of intrusion) see chapter 4), after being triggered by an eruption-related earthquake.

Thistle Slide (1983): Starting in April of 1983 and continuing into May of that year, a slow-moving traveled 305 m (1,000 ft) downhill and blocked Spanish Fork Canyon with an dam 61 m (200 ft) high. This caused disastrous flooding upstream in the Soldier Creek and Thistle Creek valleys, submerging the town of Thistle. As part of the emergency response, a spillway was constructed to prevent the newly formed lake from breaching the dam. Later, a tunnel was constructed to drain the lake, and currently the continues to flow through this tunnel. The rail line and US-6 highway had to be relocated at a cost of more than $200 million.

Rockville Rock Fall (2013): Rockville, Utah is a small community near the entrance to Zion National Park. In December of 2013, a 2,700 ton (1,400 yd3) block of Shinarump fell from the Rockville Bench cliff, landed on the steep 35-degree slope below, and shattered into several large pieces that continued downslope at a high speed. These boulders completely destroyed a house located 375 feet below the cliff (see the before and after photographs) and killed two people inside the home. The topographic map shows other rock in the area prior to this catastrophic event.
North Salt Lake Slide (2014): In August 2014 after a particularly wet , a slow moving rotational destroyed one home and damaged nearby tennis courts.

Reports from residents suggested that ground cracks had been seen near the top of the slope at least a year prior to the catastrophic movement. The presence of easily-drained sands and gravels overlying more impermeable clays weathered from , along with recent regrading of the slope, may have been contributing causes of this slide. Local heavy rains seem to have provided the . In the two years after the , the slope has been partially regraded to increase its stability. Unfortunately, in January 2017, parts of the slope have shown reactivation movement. Similarly, in 1996 residents in a nearby subdivision started reporting distress to their homes. This distress continued until 2012 when 18 homes became uninhabitable due to extensive damage and were removed. A geologic park was constructed in the now vacant area.
Video 10.3: North Salt Lake landslide.
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Bingham Canyon Copper Mine Landslide, Utah (2013): At 9:30 pm on April 10, 2013, more than 65 million cubic meters of steep terraced wall slid down into the engineered pit of Bingham Canyon , making it one of the largest historic not associated with . Radar systems maintained by the operator warned of movement of the wall, preventing the loss of life and limiting the loss of property.
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Summary
is a geologic term describing all downhill rock and movement due to gravity. occurs when a slope is too steep to remain stable with existing material and conditions. Loose rock and , called , are what typically move during a mass-wasting event. Slope stability is determined by two factors: the angle of the slope and the of the accumulated materials. Mass-wasting events are triggered by changes that slope angles and weaken slope stability, such as rapid snow melt, intense rainfall, earthquake shaking, eruption, storm waves, , and human activities. Excessive is the most common trigger. Mass-wasting events are classified by their type of movement and material, and they share common morphological surface features. The most common types of mass-wasting events are , slides, flows, and .
Mass-wasting movement ranges from slow to dangerously rapid. Areas with steep topography and rapid rainfall, such as the California coast, Rocky Mountain Region, and Pacific Northwest, are particularly susceptible to hazardous mass-wasting events. By examining examples and lessons learned from famous mass-wasting events, scientists have a better understanding of how mass-wasting occurs. This knowledge has brought them closer to predicting where and how these potentially hazardous events may occur and how people can be protected.
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Text References
- Haugerud, R.A., 2014, Preliminary interpretation of pre-2014 landslide deposits in the vicinity of Oso, Washington: US Geological Survey.
- Highland, L., 2004, Landslide types and processes: pubs.er.usgs.gov.
- Highland, L.M., and Bobrowsky, P., 2008, The Landslide Handbook – A Guide to Understanding Landslide: U.S. Geological Survey USGS Numbered Series 1325, 147 p.
- Highland, L.M., and Schuster, R.L., 2000, Significant landslide events in the United States: United States Geological Survey.
- Hildenbrand, T.G., and Hendricks, J.D., 1995, Geophysical setting of the Reelfoot rift and relations between rift structures and the New Madrid seismic zone: U.S. Geological Survey Professional Paper 1538-E, 36 p.
- Hungr, O., Leroueil, S., and Picarelli, L., 2013, The Varnes classification of landslide types, an update: Landslides, v. 11, no. 2, p. 167–194.
- Jibson, R.W., 2005, Landslide hazards at La Conchita, California: United States Geological Survey Open-File Report 2005-1067.
- Lipman, P.W., and Mullineaux, D.R., 1981, The 1980 eruptions of Mount St. Helens, Washington: US Geological Survey USGS Numbered Series 1250, 844 p., doi: 10.3133/pp1250.
- Lund, W.R., Knudsen, T.R., and Bowman, S.D., 2014, Investigation of the December 12, 2013, Fatal Rock Fall at 368 West Main Street, Rockville, Utah: Utah Geological Survey 273, 24 p.
- United States Forest Service, 2016, A Brief History of the Gros Ventre Slide Geological Site: United States Forest Service.
Figure References
Figure 10.1: Forces on a block on an inclined plane (fg = force of gravity; fn = normal force; fs = shear force). Kindred Grey. 2022. CC BY 4.0. Includes crate by Andrew Doane from Noun Project (Noun Project license).
Figure 10.2: As slope increases, the force of gravity (fg) stays the same and the normal force decreases while the shear force proportionately increases. Kindred Grey. 2022. CC BY 4.0. Includes crate by Andrew Doane from Noun Project (Noun Project license).
Figure 10.3: Angle of repose in a pile of sand. Captain Sprite. 2007. CC BY-SA 2.5. https://en.wikipedia.org/wiki/File:Angleofrepose.png
Figure 10.4: Locations A and B have bedding nearly perpendicular to the slope, making for a relatively stable slope. Location D has bedding nearly parallel to the slope, increasing the risk of slope failure. Location C has bedding nearly horizontal and the stability is relatively intermediate. Kindred Grey. 2022. CC BY 4.0.
Figure 10.5: Examples of some of the types of landslides. R.L. Schuster, U.S. Geological Survey. 2004. Public domain. https://pubs.usgs.gov/fs/2004/3072/fs-2004-3072.html
Figure 10.6: Scar of the Gros Ventre landslide in background with landslide deposits in the foreground. Daniel Mayer. 2006. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Gros_Venture_Slide.JPG
Figure 10.7: Grand Teton National Park showing sedimentary layers parallel with the surface and undercutting (oversteepening) of the slope by the river. Daniel Mayer. 2006. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Lower_Slide_Lake.JPG
Figure 10.8: Road damage from the August 1959 Hebgen Lake (Montana-Yellowstone) earthquake. R.B. Colton via USGS. 1959. Public domain. https://commons.wikimedia.org/wiki/File:Roaddamage59quake.JPG
Figure 10.9: Oblique LIDAR image of La Conchita after the 2005 landslide. Todd Stennett via USGS. 2016. Public domain. https://www.usgs.gov/media/images/la-conchita
Figure 10.10: 1995 La Conchita slide. USGS. 2005. Public domain. https://commons.wikimedia.org/wiki/File:Laconchita1995landslide.jpg
Figure 10.11: 2014 Oso slide in Washington killed 43 people and buried many homes. Mark Reid, USGS. 2014. Public domain. https://commons.wikimedia.org/wiki/File:Oso_Landslide_aerial.jpg
Figure 10.12: Annotated Lidar map of 2014 Oso slide in Washington. USGS. 2014. Public domain. https://commons.wikimedia.org/wiki/File:Oso_landslide_geomorphology_map.png
Figure 10.13: Approximate extent of Markagunt gravity slide. Used under fair use from THE EARLY MIOCENE MARKAGUNT MEGABRECCIA: UTAH’S LARGEST CATASTROPHIC LANDSLIDE by Robert F. Biek. https://geology.utah.gov/map-pub/survey-notes/the-early-miocene-markagunt-megabreccia/
Figure 10.14: The 1983 Thistle landslide (foreground) dammed the Spanish Fork river creating a lake. R.L. Schuster, U.S. Geological Survey. 1983. Public domain. https://en.wikipedia.org/wiki/File:Thistlelandslideusgs.jpg
Figure 10.15: House before and after destruction from 2013 Rockville rockfall. Used under fair use from INVESTIGATION OF THE DECEMBER 12, 2013,FATAL ROCK FALL AT 368 WEST MAIN STREET, ROCKVILLE, UTAH by William R. Lund, Tyler R. Knudsen, and Steve D. Bowman. https://ugspub.nr.utah.gov/publications/reports_of_investigations/ri-273.pdf
Figure 10.16: Scarp and displaced material from the North Salt Lake (Parkview) slide of 2014. Used under fair use from PARKWAY DRIVE LANDSLIDE, NORTH SALT LAKE. https://geology.utah.gov/hazards/landslides/parkway_drive_landslide/
Any downhill movement of material, caused by gravity.
General term for sudden material falling (sliding) down a slope due to gravity.
A type of non-eroded sediment mixed with organic matter, used by plants. Many essential elements for life, like nitrogen, are delivered to organisms via the soil.
Term for the underlying lithified rocks that make up the geologic record in an area. This term can sometimes refer to only the deeper, crystalline (non-layered) rocks.
Detached, free-falling rocks from very steep slopes.
A mixture of coarse material and water, channeled and flowing downhill rapidly.
Stress within an object that causes a side-to-side movement within an internal fabric or weakness.
Component of the gravitational force which pushes material downslope.
Component of the gravitational force which holds material on a slope.
The relationship between shear force and normal force in a block of material on a slope. When shear force is greater than normal force, mass wasting can occur.
Slope angle where shear forces and normal forces are equal.
The average diameter of a grain of sediment, ranging from small, also known as fine-grained (e.g. clay, silt) to large, also known as coarse-grained (e.g. boulder).
The mineral makeup of a rock, i.e. which minerals are found within a rock.
Empty space in a geologic material, either within sediments, or within rocks. Can be filled by air, water, or hydrocarbons.
Pieces of rock that have been weathered and possibly eroded.
Discernible layers of rock, typically from a sedimentary rock.
A volcanic rock with medium silica composition, equally rich in felsic minerals (feldspar) and mafic minerals (amphibole, biotite, pyroxene). Intermediate rocks are grey in color and contain somewhat equal amounts of minerals that are light and dark in color. Primary intermediate rocks are andesite (extrusive) and diorite (intrusive).
A natural substance that is typically solid, has a crystalline structure, and is typically formed by inorganic processes. Minerals are the building blocks of most rocks.
A very fine-grained rock with very thin layering (fissile).
A solution that has the maximum allowed dissolved component, and is unable to dissolve more.
An event that causes a landslide event. Water is a common trigger.
Place where lava is erupted at the surface.
The transport and movement of weathered sediments.
A sequence of layers in which the sediment changes linearly in size, either getting coarser or finer.
The act of a solid coming out of solution, typically resulting from a drop in temperature or a decrease of the dissolving material.
A channelled body of water.
Water that flows over the surface.
Water that works its way down into the subsurface.
A slope, that by natural or human activity, becomes steeper than the angle of repose.
An exposed part of a craton.
Loose blocks of rock that fall down from steep surfaces and cover slopes.
A landslide that moves along an internal plane of weakness.
A slow and steady movement. Can occur as part of faults, mass wasting, and grain movement.
A break within a rock that has no relative movement between the sides. Caused by cooling, pressure release, tectonic forces, etc.
The physical breakdown (weathering) of bedrock by processes such as pressure, ice expansion, etc.
Movement of regolith along a curved slip plane.
Plastic moving, fine-grained type of flow.
Large and mysterious landslides that travel for long distances.
Ridges of sediment that form perpendicular to flow in the lower part of the lower flow regime.
Very slow movement of the soil downhill.
The measure of degrees north or south from the equator, which has a latitude of 0 degrees. The Earth's north and south poles have latitudes of 90 degrees north and south, respectively.
Sediment gathering together and collecting, typically in a topographic low point.
The act of gathering new information from the senses or from a scientific instrument.
Amount of movement during a faulting event.
Place where fault movement cuts the surface of the Earth.
Stresses that pull objects apart into a larger surface area or volume; stretching forces.
The area within a topographic basin or drainage divide in which water collects.
A rock primarily made of sand.
A measure of earthquake strength. Scales include Richter and Moment.
A planar alignment of minerals and textures within a rock.
Rocks formed via heat and/or pressure which change the minerals within the rock.
A type of volcanic mudslide, in which rain or snowmelt accumulates volcanic ash of the slopes of steep volcanoes or other mountains and then wash downhill, causing damaging flooding.
Water that is below the surface.
A unit of the geologic time scale; smaller than an era, larger than an epoch. We are currently in the Quaternary period.
The theory that the outer layer of the Earth (the lithosphere) is broken in several plates, and these plates move relative to one another, causing the major topographic features of Earth (e.g. mountains, oceans) and most earthquakes and volcanoes.
Force applied to an object, typically dealing with forces within the Earth.
A type of mechanical weathering in which outer layers of rock, approximately parallel to the surface, fracture off.
A process where water freezes inside cracks in rocks, causing expansion and mechanical weathering.
General name of a felsic rock that is intrusive. Has more felsic minerals than mafic minerals.
A sedimentary rock with rounded, larger (≥2 mm) clasts.
Planar feature where two blocks of bedrock move past each other via earthquakes.
A narrow igneous intrusion that cuts through existing rock, not along bedding planes.
Large igneous intrusion that is wedged between sedimentary layers, bulging upwards. Called a lopolith if bulging downward.
Rocks that are formed from liquid rock, i.e. from volcanic processes.
Volcanic tephra that is less than 2 mm in diameter.
Place where material is extracted from the Earth for human use.
Loose material that is a mixture of soil components and weathered bedrock sediments.