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34-588: The river has carried rock debris , soil and parts of trees and plants from the mountain range of Aroania (also known as Chelmos, Χελμός), to deposit it in the valley. This occurs mainly in the wet seasons of the Quaternary. In addition, the Scree (rock fragments) from the surrounding mountains formed further layers of sediment in the valley. The surface of the valley was gradually covered by layers of clayish, fertile soil. Valley and river achieved their modern form. People of

68-410: A gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics . It occurs both naturally and artificially . As an example of the latter, a "major commercial application of liquefaction is the liquefaction of air to allow separation of the constituents, such as oxygen, nitrogen, and the noble gases." Another is the conversion of solid coal into a liquid form usable as

102-401: A Liar , choreographer David Gordon brought together the music of Harry Partch and the words of John McPhee from The Control of Nature , read by Norma Fire, in a dance titled "Debris Flow", a "harrowing taped narrative of a family's ordeal in a massive L.A. mudslide..." Liquefaction In materials science , liquefaction is a process that generates a liquid from a solid or

136-410: A dangerous shift in the load. In physics and chemistry , the phase transitions from solid and gas to liquid ( melting and condensation , respectively) may be referred to as liquefaction. The melting point (sometimes called liquefaction point) is the temperature and pressure at which a solid becomes a liquid. In commercial and industrial situations, the process of condensing a gas to liquid

170-408: A debris-flow surge often contains an abundance of coarse material such as boulders and logs that impart a great deal of friction . Trailing behind the high-friction flow head is a lower-friction, mostly liquefied flow body that contains a higher percentage of sand , silt and clay. These fine sediments help retain high pore-fluid pressures that enhance debris-flow mobility. In some cases the flow body

204-438: A huge amount of karst water after a fairly short distance. They feed River Aroanios. A detailed international geological study lists 41 of these spring outlets. According to this study the waters of the outlets emerge directly from local karstic rock layers, which outcrop here, or they rise from the loose Sedimentation ( Silicate minerals , sand and gravel ). Rainbow trout farms, restaurants and displays of tourist ware crowd

238-418: A last resort because they are expensive to construct and require commitment to annual maintenance. Also, debris basins may only retain debris flows from a fraction of streams that drain mountainous terrain. Before a storm that can potentially nucleate debris flows, forecasting frameworks can often quantify the likelihood that a debris flow might occur in a watershed; however, it remains challenging to predict

272-514: A liquid, for example in food preparation or laboratory use. This may be done with a blender, or liquidiser in British English. Liquefaction of silica and silicate glasses occurs on electron beam irradiation of nanosized samples in the column of transmission electron microscope. In biology , liquefaction often involves organic tissue turning into a more liquid-like state. For example, liquefactive necrosis in pathology , or liquefaction as

306-706: A result of their high sediment concentrations and mobility, debris flows can be very destructive. Notable debris-flow disasters of the twentieth century involved more than 20,000 fatalities in Armero, Colombia , in 1985 and tens of thousands in Vargas State , Venezuela , in 1999. Debris flows have volumetric sediment concentrations exceeding about 40 to 50%, and the remainder of a flow's volume consists of water. By definition, “debris” includes sediment grains with diverse shapes and sizes, commonly ranging from microscopic clay particles to great boulders . Media reports often use

340-647: A significant hazard in many steep, mountainous areas, and have received particular attention in Japan, China, Taiwan, USA, Canada, New Zealand, the Philippines, the European Alps, Russia, and Kazakhstan. In Japan a large debris flow or landslide is called yamatsunami ( 山津波 ), literally mountain tsunami . Debris flows are accelerated downhill by gravity and tend to follow steep mountain channels that debouche onto alluvial fans or floodplains . The front, or 'head' of

374-399: A strong coupling between the solid and the fluid momentum transfer , where the solid's normal stress is reduced by buoyancy , which in turn diminishes the frictional resistance, enhances the pressure gradient , and reduces the drag on the solid component. Buoyancy is an important aspect of two-phase debris flow, because it enhances flow mobility (longer travel distances) by reducing

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408-461: A substitute for liquid fuels. In geology , soil liquefaction refers to the process by which water-saturated, unconsolidated sediments are transformed into a substance that acts like a liquid, often in an earthquake. Soil liquefaction was blamed for building collapses in the city of Palu, Indonesia in October 2018. In a related phenomenon, liquefaction of bulk materials in cargo ships may cause

442-434: Is a debris flow related in some way to volcanic activity , either directly as a result of an eruption, or indirectly by the collapse of loose material on the flanks of a volcano. A variety of phenomena may trigger a lahar, including melting of glacial ice, sector collapse , intense rainfall on loose pyroclastic material, or the outburst of a lake that was previously dammed by pyroclastic or glacial sediments. The word lahar

476-477: Is followed by a more watery tail that transitions into a hyperconcentrated stream flow. Debris flows tend to move in a series of pulses, or discrete surges, wherein each pulse or surge has a distinctive head, body and tail. Debris-flow deposits are readily recognizable in the field. They make up significant percentages of many alluvial fans and debris cones along steep mountain fronts. Fully exposed deposits commonly have lobate forms with boulder-rich snouts, and

510-528: Is of Indonesian origin, but is now routinely used by geologists worldwide to describe volcanogenic debris flows. Nearly all of Earth's largest, most destructive debris flows are lahars that originate on volcanoes. An example is the lahar that inundated the city of Armero , Colombia. A jökulhlaup is a glacial outburst flood. Jökulhlaup is an Icelandic word, and in Iceland many glacial outburst floods are triggered by sub-glacial volcanic eruptions. (Iceland sits atop

544-434: Is sometimes referred to as liquefaction of gases . Coal liquefaction is the production of liquid fuels from coal using a variety of industrial processes. Liquefaction is also used in commercial and industrial settings to refer to mechanical dissolution of a solid by mixing , grinding or blending with a liquid. In kitchen or laboratory settings, solids may be chopped into smaller parts sometimes in combination with

578-426: Is “Katsana”. Pausanias (110-180 AD) in his book “Description of Greece” (Ancient Greek: Ἑλλάδος Περιήγησις) already used the name “Aroanios” for the valley's river. The preserved publications of Polybios (208-125 BC, “Historíai”) and of Pliny The Elder (AD 23-79, “Naturalis historia”) confirm Pausanias’ description, but are less precise and informative. Aroanios is the river's official name. But at some point in

612-527: The Mid-Atlantic Ridge, which is formed by a chain of mostly submarine volcanoes). Elsewhere, a more common cause of jökulhlaups is the breaching of ice-dammed or moraine -dammed lakes. Such breaching events are often caused by the sudden calving of glacier ice into a lake, which then causes a displacement wave to breach a moraine or ice dam. Downvalley of the breach point, a jökulhlaup may increase greatly in size through entrainment of loose sediment from

646-422: The amount of sediment mobilized and therefore, the total size of debris flows that may nucleate for a given storm, and whether or not debris basins will have the capacity to protect downstream communities. These challenges make debris flows particularly dangerous to mountain front communities. In 1989, as part of his large-scale piece David Gordon's United States , and later, in 1999, as part of Autobiography of

680-444: The chief conditions required for debris flow initiation include the presence of slopes steeper than about 25 degrees , the availability of abundant loose sediment, soil, or weathered rock, and sufficient water to bring this loose material to a state of almost complete saturation (with all the pore space filled). Debris flows can be more frequent following forest and brush fires, as experience in southern California demonstrates. They pose

714-512: The effective frictional shear stress for the solid phase is that of pure granular flow. In this case the force due to the pressure gradient is altered, the drag is high and the effect of the virtual mass disappears in the solid momentum. All this leads to slowing down the motion . To prevent debris flows reaching property and people, a debris basin may be constructed. Debris basins are designed to protect soil and water resources or to prevent downstream damage. Such constructions are considered to be

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748-513: The fluid and the solid phases. The effect is substantial when the density ratio ( γ {\displaystyle \gamma } ) is large (e.g., in the natural debris flow). If the flow is neutrally buoyant, i.e., γ = 1 {\displaystyle \gamma =1} , (see, e.g., Bagnold, 1954) the debris mass is fluidized and moves longer travel distances. This can happen in highly viscous natural debris flows. For neutrally buoyant flows, Coulomb friction disappears,

782-997: The fragile nature (see the photographic document). Debris flow Debris flows are geological phenomena in which water-laden masses of soil and fragmented rock flow down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally have bulk densities comparable to those of rock avalanches and other types of landslides (roughly 2000 kilograms per cubic meter), but owing to widespread sediment liquefaction caused by high pore-fluid pressures , they can flow almost as fluidly as water. Debris flows descending steep channels commonly attain speeds that surpass 10 m/s (36 km/h), although some large flows can reach speeds that are much greater. Debris flows with volumes ranging up to about 100,000 cubic meters occur frequently in mountainous regions worldwide. The largest prehistoric flows have had volumes exceeding 1 billion cubic meters (i.e., 1 cubic kilometer). As

816-424: The frictional resistance in the mixture . Buoyancy is present as long as there is fluid in the mixture. It reduces the solid normal stress, solid lateral normal stresses, and the basal shear stress (thus, frictional resistance) by a factor ( 1 − γ {\displaystyle 1-\gamma } ), where γ {\displaystyle \gamma } is the density ratio between

850-432: The lateral margins of debris-flow deposits and paths are commonly marked by the presence of boulder-rich lateral levees . These natural levees form when relatively mobile, liquefied, fine-grained debris in the body of debris flows shoulders aside coarse, high-friction debris that collects in debris-flow heads as a consequence of grain-size segregation (a familiar phenomenon in granular mechanics ). Lateral levees can confine

884-483: The lateral solid pressure gradient vanishes, the drag coefficient is zero, and the basal slope effect on the solid phase also vanishes. In this limiting case , the only remaining solid force is due to gravity , and thus the force associated with buoyancy. Under these conditions of hydrodynamic support of the particles by the fluid, the debris mass is fully fluidized (or lubricated ) and moves very economically, promoting long travel distances. Compared to buoyant flow,

918-401: The neutrally buoyant flow shows completely different behaviour. For the latter case, the solid and fluid phases move together, the debris bulk mass is fluidized, the front moves substantially farther, the tail lags behind, and the overall flow height is also reduced. When γ = 0 {\displaystyle \gamma =0} , the flow does not experience any buoyancy effect. Then

952-555: The past the river bore the name Katzanas or Katsanas (Κατσάνας, en: Katzánas). The cited ancient book authors also report on the antique city Cleitor as predecessor of modern Kleitoria - again Pausanias is the most precise. Wall remnants are still visible in the valley only 1300m west of the modern town. At Kleitoria's position - in the middle of the broad valley - the three small river waters merge with River Aroanios. The River Aroanios must not be confused with another, smaller river of

986-795: The paths of ensuing debris flows, and the presence of older levees provides some idea of the magnitudes of previous debris flows in a particular area. Through dating of trees growing on such deposits, the approximate frequency of destructive debris flows can be estimated. This is important information for land development in areas where debris flows are common. Ancient debris-flow deposits that are exposed only in outcrops are more difficult to recognize, but are commonly typified by juxtaposition of grains with greatly differing shapes and sizes. This poor sorting of sediment grains distinguishes debris-flow deposits from most water-laid sediments. Other geological flows that can be described as debris flows are typically given more specific names. These include: A lahar

1020-486: The same name. That river flows generally southwest bound and pours into River Erymanthos at the community Psofida . The karst springs of River Aroanios (for other karst springs on the Peloponnese see el:Καρστική πηγή ) emerge in a small forest of „ plane trees “ (580x30m) next to the village of Planitero (Achaea). The plane trees obviously benefit from the karst springs water. The very small outlets together issue

1054-867: The term mudflow to describe debris flows, but true mudflows are composed mostly of grains smaller than sand . On Earth's land surface, mudflows are far less common than debris flows. However, underwater mudflows are prevalent on submarine continental margins , where they may spawn turbidity currents . Debris flows in forested regions can contain large quantities of woody debris such as logs and tree stumps. Sediment-rich water floods with solid concentrations ranging from about 10 to 40% behave somewhat differently from debris flows and are known as hyperconcentrated floods. Normal stream flows contain even lower concentrations of sediment. Debris flows can be triggered by intense rainfall or snowmelt, by dam-break or glacial outburst floods, or by landsliding that may or may not be associated with intense rain or earthquakes. In all cases

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1088-624: The valley through which it travels. Ample entrainment can enable the flood to transform to a debris flow. Travel distances may exceed 100 km. Numerous different approaches have been used to model debris-flow properties, kinematics , and dynamics . Some are listed here. Calibrating and validating such sophisticated models require well-documented data from field surveys or minute laboratory experiments. The mixture theory , originally proposed by Iverson and later adopted and modified by others, treats debris flows as two-phase solid-fluid mixtures. In real two-phase (debris) mass flows there exists

1122-466: The villages and small towns cultivated the ground. At the confluence of the small rivers Λαγκάδα, Ξηρόρεμα and Kleitoras , coming from the carbonate mountains in the west, their alluvial fan expanded the valley drastically. Here, on a hill in the widened valley, the largest town of the valley has developed: Kleitoria . The local residents turned the whole valley into a picturesque, beautiful Cultural landscape with fields, gardens and many trees. Its name

1156-562: The whole area. In summer the forest is part of an excursion for residents, who come in busses and private cars even from Patras , despite the long distance. The springs under the wooded area are an extraordinaryly valuable piece of nature - a true “ Geotope “ - rare not only in Greece. It ought to be preserved and protected accordingly (see also the photo). But the natural monument is dominated by to much commercial tourism. Verandas of restaurants, sale points, an abandoned buildings stand directly in

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