Arête

An arête is a thin, almost knife-like, ridge of rock which is typically formed when two glaciers erode parallel U-shaped valleys. The arête is a thin ridge of rock that is left separating the two valleys. Arêtes can also form when two glacial cirques erode headwards towards one another, although frequently this results in a saddle-shaped pass, called a col. The edge is then sharpened by freeze-thaw weathering. The word "arête" is actually French for fishbone; similar features in the Alps are described with the German equivalent term Grat or Kamm (comb).

Where three or more cirques meet, a pyramidal peak is created.

Cleaver

A cleaver is a type of arête that separates a unified flow of glacial ice from its uphill side into two glaciers flanking, and flowing parallel to, the ridge. Cleaver gets its name from the way it resembles a meat cleaver slicing meat into two parts. A cleaver may be thought of as analogous to an island in a river. A common situation has the two flanking glaciers melting to their respective ends before their courses can bring them back together; the exceedingly rare analogy is a situation of the two branches of a river drying up, before the downstream tip of the island, by evaporation or absorption into the ground.

The location of a cleaver is often an important factor in the choice among routes for glacier flow. For example, following a cleaver up or down a mountain may avoid travelling on or under an unstable glacial, snow, or rock area. This is usually the case on those summer routes to the summit whose lower portions are on the south face of Mount Rainier: climbers traverse the "flats" of Ingraham Glacier, but ascend Disappointment Cleaver and follow its ridgeline rather than ascending the headwall either of that glacier or (on the other side of the cleaver) of Emmons Glacier.

Examples

Notable examples of arêtes include:

* Knife Edge, on Mount Katahdin, Maine
* Clouds Rest, in the Sierra Nevada, California
* The Minarets, in the Sierra Nevada, California
* The Garden Wall, in Glacier National Park, Montana
* Crib Goch, in Snowdonia National Park, Wales
* Striding Edge in the English Lake District
* The Catwalk, in the Olympic National Park, state of Washington

Anchor (climbing)

In rock climbing, an anchor can be any way of attaching the climber, the rope, or a load to rock, ice, steep dirt, or a building by either permanent or temporary means. The goal of an anchor depends on the type of climbing under consideration but usually consists of stopping a fall, or holding a static load.

Types of anchors

Depending on the material being climbed, there are many types of protection that can be used to construct the anchor, including natural protection such as boulders and trees, or artificial protection such as cams, nuts, bolts or pitons.

Natural anchor

A natural anchor is one that does not require man-made climbing gear. Such anchors may consist of trees, chockstones already lodged in a crack, horns and protrusions, etc.

Artificial anchor

An artificial anchor consists of man-made climbing gear placed in the rock. Such gear may be spring loaded camming devices, aluminum chockstones, steel expansion bolts, pitons, etc.

Belay anchor

A belay anchor is used as a sole attachment to the cliff face, to support a belay or toprope. It should ideally be essentially foolproof, consisting of multiple redundant components (natural and/or artificial), none of which are likely to fail, and none of which in the event of failure would cause the entire anchor to fail. Any one component of a good anchor should be able to support the entire system by itself.

Running belay anchor

A running belay anchor is used as a safeguard in the event of a fall while lead climbing. Often hastily placed in the stress of the moment, these anchors are not as secure, or bombproof as belay anchors and cannot be relied on as sole attachment points to the rock. Running belay anchors must be backed up by other running belay anchors below should they fail.

Ice anchors

The ice picket is used as an anchor in mountaineering. It is driven into the snow and used to arrest falls.


Attachment to the anchor

Indirect

When the rope goes from the climber to the belayer. Most often used under controlled circumstances at climbing walls or when the climber doesn't have the weight advantage on the belayer during bottom roped climbs. It is impossible to escape from the system.

Semi-direct

When the rope comes from the climber to the belayer, but the belayer is attached separately to an anchor. Often used when multi pitching and the belayer is on a stance. Or when top roping and it is possible that if the climber falls the belayer will be pulled from the stance above the climber. The belayer can, with a little effort then remove themselves from the system if required. it is essential that the belayer is attached to the anchor via the belay loop at the front of the harness. Attaching the belayers harness to the anchor via the back of the harness can cause the harness, when placed under strain constrict inwards elongating front to back, rather than side to side. This can result in crushed pelvis' and serious harm to the belayer.

Direct

When the rope comes from the climber to an anchor. A hanging belay device may be used, although it is common in this instance to just use an Italian hitch. The belayer is totally free of the system.


Equalization

Anchor equalization is the process of combining two or more anchors in the build of a single equalized anchor. This is the method used in a redundant belay anchor, as mentioned above. If assembled correctly, the load can be distributed amongst the individual anchors, rather than placing all the load on a single anchor point. This decreases the chance that any of the anchor points will fail, and, if a point does fail, the other(s) should still be able to hold.

When forming an equalized anchor, it is important to take into consideration the angle formed between the two pieces of protection -- the "V-angle". One must try to minimize this angle as much as possible, because the greater the V-angle, the more force will be placed on each piece of protection. As shown below, if the V-angle is greater than 120 degrees, the load on each anchor comprising the equalized anchor will actually be greater than the load on the rope connected to the equalized anchor. This is a hazardous situation which makes it worse to use equalization than not at all, and should be avoided.

If the load force (To load in the image at right) is FLoad and the V-angle is θV, then the force on each anchor is given by:

Resulting from this expression, we can deduce:

* At a V-angle of 30 degrees, each of the two anchors bear a force of about 52% of the original load.
* At 45 degrees, each anchor bears about 54% of the load.
* At 60 degrees, each anchor bears about 58% of the load.
* At 90 degrees, each anchor bears about 71% of the load.
* At 120 degrees, each anchor bears a force equivalent to 100% of the original load. An angle this large should never be used.

Alpine style

Alpine style refers to mountaineering in a self-sufficient manner, thereby carrying all of one's food, shelter, equipment etc. as one climbs, as opposed to expedition style (or siege style) mountaineering which involves setting up a fixed line of stocked camps on the mountain which can be accessed at one's leisure. Additionally, alpine style means the refusal of fixed ropes, high altitude porters and the use of supplemental oxygen.

Many consider Alpine style to be the purest form of mountaineering, setting a standard to which all mountaineers should aspire. This style became well-known and popular with Reinhold Messner, when he and Peter Habeler climbed Gasherbrum I without oxygen equipment in 1975. It was Hermann Buhl's idea to demonstrate Alpine style in the Karakoram at the successful Austrian Broad Peak expedition in 1957; in pure Alpine style the members of this expedition later climbed Skil Brum (Marcus Schmuck and Fritz Wintersteller) and approached Chogolisa (Hermann Buhl and Kurt Diemberger).

The benefits of alpine style are that, generally, much less time is spent on the route, reducing objective dangers such as avalanches or blizzards. This can be a major factor on routes with ice fields full of blocks of ice hundreds of feet tall which could fall at any time. Snow and ice conditions often change over the course of a day forcing climbing parties to climb in the early hours before the sun melts the snow or ice making it unsuitable and more susceptible to avalanche. This tendency to climb in the morning has led to the term "Alpine Start". An "Alpine Start" is a start that happens in the early morning ranging from 11:00 PM on long routes to not long before sunrise for shorter routes or faster parties. An "Alpine Start" must begin in the dark.

The problems encountered while alpine style climbing are related to lack of support. Without fixed ropes to retreat down in case of emergency, or a lower camp to return to, the commitment of alpine style is greater than expedition style in terms of the choice to ascend or descend. A climbing group caught at a point where conditions do not allow further ascent must consider other options such as an unplanned bivouac (perhaps without the appropriate gear), rappels (leaving multiple pieces of protection behind), or moving to another route from their current position (perhaps without adequate knowledge of the alternative route). However, alpine style often is cheaper and faster for those on a budget.

Mountain hut

A Mountain hut (also known as alpine hut, mountain shelter, and mountain hostel) is a building located in the mountains intended to provide food and shelter to mountaineers, climbers and hikers. Mountain huts are usually operated by a section of an Alpine Club. Most mountain huts are tended to by Alpine Club personnel throughout the mountaineering season, who prepare meals and drinks for mountaineers, similar to a restaurant, but usually with a limited selection, as it is not always easy to transport the food to the hut. Furthermore, mountain huts provide simple sleeping berths. Any mountaineer is allowed to access Alpine huts, but members of an Alpine Club usually get a discount. Some huts in more remote areas have no personnel, but mountaineers are allowed to access them.

As there is a lot of mountaineering activity in the Alps, there is a large number of huts along the mountaineering paths. One cannot necessarily count on finding a similarly dense network of paths and huts in other mountain ranges.

In the United Kingdom and Ireland the tradition is of unwardened "climbing huts" providing fairly rudimentary accommodation (but superior to that of a bothy) close to a climbing ground; the huts are usually conversions (eg of former quarrymen's cottages, or of disused mine buildings), and are not open to passers-by except in emergency. Many climbing clubs in the UK have such huts in Snowdonia or in the Lake District. A well-known example is the 'Charles Inglis Clark Memorial Hut' (the 'CIC Hut') under the northern crags of Ben Nevis in Scotland - this is a purpose-built hut, high up the mountain, probably nearest in character to the Alpine huts.

Altitude sickness

Altitude sickness, also known as acute mountain sickness (AMS), altitude illness, or soroche, is a pathological condition that is caused by acute exposure to low air pressure (usually outdoors at high altitudes). It commonly occurs above 2,400 metres (approximately 8,000 feet). Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE).

The cause of altitude sickness is still not understood. It occurs in low atmospheric pressure conditions but not necessarily in low oxygen conditions at sea level pressure. Although treatable to some extent by the administration of oxygen, most of the symptoms do not appear to be caused by low oxygen, but rather by the low CO2 levels causing a rise in blood pH, alkalosis. The percentage of oxygen in air remains essentially constant with altitude at 21 percent, but the air pressure (and therefore the number of oxygen molecules) drops as altitude increases. Altitude sickness usually does not affect persons traveling in aircraft because modern aircraft passenger compartments are pressurized.

A related condition, occurring only after prolonged exposure to high altitude, is chronic mountain sickness, also known as Monge's disease.

An unrelated condition, although often confused with altitude sickness, is dehydration, due to the higher rate of water vapor lost from the lungs at higher altitudes.

Introduction

High altitude or mountain sickness is defined when someone feels sick at high altitudes, such as in the mountains or any other altitude-related sicknesses. It is hard to determine who will be affected by altitude-sickness as there are no specific factors that compare with this susceptibility to altitude sickness. However, most people can climb up to 2500 meters (8000 feet) normally.

Generally, different people have different susceptibilities to altitude sickness. For some otherwise healthy people, Acute Mountain Sickness (AMS) can begin to appear at around 2000 meters (6,500 feet) above sea level, such as at many mountain ski resorts, equivalent to a pressure of 80 kPa. AMS is the most frequent type of altitude sickness encountered. Symptoms often manifest themselves 6-10 hours after ascent and generally subside in 1 to 2 days, but they occasionally develop into the more serious conditions. Symptoms include headache, fatigue, stomach illness, dizziness, and sleep disturbance. Exertion aggravates the symptoms.

High altitude pulmonary edema (HAPE) and cerebral edema (HACE) are the most ominous of these symptoms, while AMS, retinal hemorrhage, and peripheral edema are less severe forms of the disease. The rate of ascent, altitude attained, amount of physical activity at high altitude, as well as individual susceptibility, are contributing factors to the onset and severity of high-altitude illness.

Altitude sickness usually occurs following a rapid ascent and can usually be prevented by ascending slowly. In most of these cases, the symptoms are temporary and usually abate as altitude acclimatisation occurs. However, in extreme cases, altitude sickness can be fatal.

The word "soroche" came from South America and originally meant "ore", because of an old, incorrect belief that it was caused by toxic emanations of ores in the Andes mountains.

Signs and symptoms

Headache is a primary symptom used to diagnose altitude sickness, although headache is also a symptom of dehydration. A headache occurring at an altitude above 2,400 meters (8000 feet = 76 kPa), combined with any one or more of the following symptoms, can indicate altitude sickness:

* Lack of appetite, nausea, or vomiting
* Fatigue or weakness
* Dizziness or light-headedness
* Insomnia
* Pins and needles
* Shortness of breath upon exertion
* Persistent rapid pulse
* Drowsiness
* General malaise
* Peripheral edema (swelling of hands, feet, and face).

Symptoms that may indicate life-threatening altitude sickness include:

* pulmonary edema (fluid in the lungs):-
o persistent dry cough
o fever
o shortness of breath even when resting
* cerebral edema (swelling of the brain):-
o headache that does not respond to analgesics
o unsteady gait
o increased vomiting
o gradual loss of consciousness.

Severe cases

The most serious symptoms of altitude sickness are due to edema (fluid accumulation in the tissues of the body). At very high altitude, humans can get either high altitude pulmonary edema (HAPE), or high altitude cerebral edema (HACE). The physiological cause of altitude-induced edema is not conclusively established. It is currently believed, however, that HACE is caused by local vasodilation of cerebral blood vessels in response to hypoxia, resulting in greater blood flow and, consequently, greater capillary pressures. On the other hand, HAPE may be due to general vasoconstriction in the pulmonary circulation (normally a response to regional ventilation-perfusion mismatches) which, with constant or increased cardiac output, also leads to increases in capillary pressures. For those suffering HACE, dexamethasone may provide temporary relief from symptoms in order to keep descending under their own power.

HAPE occurs in ~2% of those who are adjusting to altitudes of ~3000 m (10,000 feet = 70 kPa) or more. It can progress rapidly and is often fatal. Symptoms include fatigue, severe dyspnea at rest, and cough that is initially dry but may progress to produce pink, frothy sputum. Descent to lower altitudes alleviates the symptoms of HAPE.

HACE is a life threatening condition that can lead to coma or death. It occurs in about 1% of people adjusting to altitudes above ~2700 m (9,000 feet = 73 kPa). Symptoms include headache, fatigue, visual impairment, bladder dysfunction, bowel dysfunction, loss of coordination, paralysis on one side of the body, and confusion. Descent to lower altitudes may save those afflicted with HACE.

PREVENTION

Avoiding alcohol ingestion

As alcohol tends to dehydrate, avoidance in the first 24 hours at a higher altitude is optimal.

Strenous activity

People with recurrent AMS note that by avoiding strenuous activity such as skiing, hiking, etc in the first 24 hours at altitude reduces their problems.

Altitude acclimatization

Altitude acclimatisation is the process of adjusting to decreasing oxygen levels at higher elevations, in order to avoid altitude sickness. Once above approximately 3,000 meters (10,000 feet = 70 kPa), most climbers and high altitude trekkers follow the "golden rule" - climb high, sleep low. For high altitude climbers, a typical acclimatization regime might be to stay a few days at a base camp, climb up to a higher camp (slowly), then return to base camp. A subsequent climb to the higher camp would then include an overnight stay. This process is then repeated a few times, each time extending the time spent at higher altitudes to let the body adjust to the oxygen level there, a process that involves the production of additional red blood cells. Once the climber has acclimatised to a given altitude, the process is repeated with camps placed at progressively higher elevations. The general rule of thumb is to not ascend more than 300 metres (1,000 feet) per day to sleep. That is, one can climb from 3,000 (10,000 feet = 70 kPa) to 4,500 metres (15,000 feet = 58 kPa) in one day, but one should then descend back to 3,300 metres (11,000 feet = 67.5 kPa) to sleep. This process cannot safely be rushed, and this explains why climbers need to spend days (or even weeks at times) acclimatising before attempting to climb a high peak. Simulated altitude equipment that produce hypoxic (reduced oxygen) air can be used to acclimate to altitude, reducing the total time required on the mountain itself.

Altitude Acclimatization is necessary for some people who rapidly move from lower altitudes to more moderate altitudes, usually by aircraft and ground transportation over a few hours, such as from sea level to 7000 feet of many Colorado, USA mountain resorts. Stopping at an intermediate altitude overnight can reduce or eliminate a repeat episode of AMS.

Drugs

Acetazolamide may help some people to speed up the acclimatisation process when taken before arriving at altitude, and can treat mild cases of altitude sickness. A typical dose is 250mg twice daily starting the day before moving to altitude.

A single randomized controlled trial found that sumatriptan may help prevent altitude sickness.

For centuries, indigenous cultures of the Altiplano, such as the Aymaras, have used coca leaves to treat mild altitude sickness.

Oxygen enrichment

In high-altitude conditions, oxygen enrichment can counteract the effects of altitude sickness, or hypoxia. A small amount of supplemental oxygen reduces the equivalent altitude in climate-controlled rooms. At 3,400 m (67 kPa), raising the oxygen concentration level by 5 percent via an oxygen concentrator and an existing ventilation system provides an effective altitude of 3,000 m (70 kPa), which is more tolerable for surface-dwellers. The most effective source of supplemental oxygen at high altitude are oxygen concentrators that use vacuum swing adsorption (VSA) technology. As opposed to generators that use pressure swing adsorption (PSA), VSA technology does not suffer from performance degradation at increased altitude. The lower air density actually facilitates the vacuum step process.

Other methods

Drinking plenty of water will also help in acclimatisation to replace the fluids lost through heavier breathing in the thin, dry air found at altitude, although consuming excessive quantities ("over-hydration") has no benefits and may lead to hyponatremia.

Oxygen from gas bottles or liquid containers can be applied directly via a nasal cannula or mask. Oxygen concentrators based upon PSA, VSA, or VPSA can be used to generate the oxygen if electricity is available. Stationary oxygen concentrators typically use PSA technology, which has performance degradations at the lower barometric pressures at high altitudes. One way to compensate for the performance degradation is to utilize a concentrator with more flow capacity. There are also portable oxygen concentrators that can be used on vehicle DC power or on internal batteries, and at least one system commercially available measures and compensates for the altitude effect on its performance up to 4,000 meters (13,123 feet). The application of high-purity oxygen from one of these methods increases the partial pressure of oxygen by raising the FIO2 (fraction of inspired oxygen).

Treatment

The only reliable treatment and in many cases the only option available is to descend. Attempts to treat or stabilise the patient in situ at altitude is dangerous unless highly controlled and with good medical facilities. However, the following treatments have been used when the patient's location and circumstances permit:

* Oxygen may be used for mild to moderate AMS below 12,000 feet and is commonly provided by physicians at mountain resorts. Symptoms abate in 12-36 hours without the need to descend.
* For more serious cases of AMS, or where rapid descent is impractical, a Gamow bag, a portable plastic pressure bag inflated with a foot pump, can be used to reduce the effective altitude by as much as 1,500 meters (5,000 feet). A Gamow bag is generally used only as an aid to evacuate severe AMS patients not to treat them at altitude.
* Acetazolamide may assist in altitude aclimatisation but is not a reliable treatment for established cases of even mild altitude sickness.
* Some claim that mild altitude sickness can be controlled by consciously taking 10-12 large, rapid breaths every 5 minutes, (hyperventilation) but this claim lacks both empirical evidence and a plausible medical reason as to why this should be effective. If overdone, this can remove too much carbon dioxide causing hypocapnia.
* The folk remedy for altitude sickness in Ecuador , Peru and Bolivia is a tea made from the coca plant. See mate de coca.
* Other treatments include injectable steroids to reduce pulmonary edema, this may buy time to descend but treats a symptom, it does not treat the underlying AMS.

Alpine butterfly knot

The Butterfly Loop, also known as the Lineman's Loop or alpine butterfly loop, is a "non-jamming loop on the bight": a loop which may be tied in a rope with two fixed ends, and can take loads on both ends of the original rope, and on the loop. The alpine butterfly loop is a symmetrical and more secure version of the butterfly loop.

Usage

The Butterfly Loop has a high breaking strength and is regarded by mountaineers as one of the strongest knots to attach climbers to the middle of a rope, such that they have room to move around even when the main rope goes tight, and they can be supported in either direction from the main rope. The loop is typically attached to a climbing harness by carabiner.

It can also be used to isolate a worn section of rope, where the knot is tied such that the worn section is used for the centre of the loop (which of course does not receive a carabiner or bears any loads in this case).

Advantages

* Does not reduce the strength of the rope by very much
* Will not slip (after initial settling)
* Allows for the knot to be loaded three ways (each end of the main line and by the loop)
* Relatively easy to undo after loading (more difficult if wet)
* Very easy to adjust the size of the bight

Disadvantages

* Difficult to tie one-handed
* Difficult to casually inspect
* Requires some training/practice to master

Single Rope Technique

Single Rope Technique (SRT) is a set of methods used to descend and ascend ropes. SRT is used in caving, potholing, rock climbing, rope rescue, roped access for building maintenance and by arborists for tree climbing.

American caver Bill Cuddington, known as "Vertical Bill", developed the SRT in the late 1950s, thus earning him the additional moniker of "father of vertical caving". The name, however, was coined by Bruce Bedford as editor of Descent magazine.

.....Technique.....

Ascent

For ascent (prusiking or "jugging"), cammed devices (ascenders) are used that can be pushed up the rope but that lock and hold the user's weight when a downward force is applied; these must also be easily removable from the rope without being detached from the user. Knots such as the Prusik, Bachmann and Klemheist are used to ascend ropes in emergencies in climbing and mountaineering; they have ceased to be the primary ascent method in SRT because they are slow in use, and ice or mud greatly reduce their efficacy.

Numerous prusik systems have been devised. Popular systems are:

* Sit-stand systems (also known as frog rig) - One ascender is at chest level attached to the sit-harness, and a second is held in the hand with a long loop of rope for the feet. Movement up the rope is by repeated moving of the foot-loop ascender up the rope, pushing up with both feet together, and sitting, supported by the chest ascender. This motion appears like a frog kick.
* Rope-walking systems - One ascender attached directly to one foot, and the second connected to the other foot by a rope with the ascender higher up to avoid clashing. Movement up the rope is by alternate stepping movements with the feet.

In general, while rope-walking techniques may be very effective for climbing long unobstructed pitches, they prove less versatile in cases of awkward passages and complex rope rigging with rebelays used to avoid hazards such as loose rocks, waterfalls, and rope damage from rub points.

Sit-stand systems are almost universally favored in Europe due to the conditions and the tradition of rigging to avoid rub points which allows for lighter weight ropes.

Many cavers in the southeastern USA favor rope-walking systems due to the enormous pitches, and have traditionally used simple rope rigging, with the rope anchored only at the top of the pitch and touching the rocks all the way down. This is sometimes pejoratively called Indestructible Rope Technique.

Descent

Descent (abseiling or rappeling) uses various forms of friction brake to control speed. The most commonly used are the Petzl Stop (self-locking) and Bobbin, and rappel racks. For safe SRT, especially on drops with complex rigging with intermediate belays, it is essential that the abseiling device can be removed from the rope without being unclipped from the harness.

Equipment

Modern SRT uses specialised devices for both descent and ascent, and low-stretch kernmantel rope of 8 mm-11 mm diameter.

Other essential items of a personal SRT set are a sit harness and one or more safety cords ("cows-tails") terminated in carabiners, for temporary attachment to safety ropes at the heads of drops and used in manoeuvres at intermediate rope belays.

Abseiling

Abseiling (German: abseilen, "to rope down"), rappelling in American English, is the controlled descent down a rope in rock climbing, mountaineering, caving, and canyoneering; the technique is used when a cliff or slope is too steep and/or dangerous to descend without protection. Abseiling is used chiefly in British English, while other Anglophone countries use different terms.

Slang terms

Slang terms for the technique include: rapping or rap jumping (American slang), abbing (British slang for "abseiling"), jumping (Australian slang), roping down, roping, seiling (Australian slang), snapling (Israeli slang), rappling (Hindi slang).

History

The origin of the abseil is attributed[2] to Jean Estéril Charlet, a Chamonix guide who lived from 1840-1925. Charlet originally devised the technique of the abseil (or rappel) method of roping down during a failed solo attempt of Petit Dru in 1876. After many attempts, some of them solo, he managed to summit the Petit Dru in 1879 in the company of two other Chamonix guides, Prosper Payot and Frédéric Folliguet, whom he hired (a rather paradoxical move for a guide). During that ascent, Charlet perfected the abseil.

Equipment

* Helmets are worn to protect the head from bumps and falling rocks. A light source may be mounted on the helmet in order to keep the hands free in unlit areas.
* Gloves protect hands from the rope and from hits with the wall. They are mainly used by recreational abseilers, industrial access practitioners, adventure racers and military as opposed to climbers or mountaineers. In fact, they can increase the risk of accident by becoming caught in the descender in certain situations.
* Boots or other sturdy footwear with good grips.
* Knee-pads (and sometimes elbow-pads) are popular in some applications for the protection of joints during crawls or hits.
* Ropes used for descending are typically of Kernmantle rope construction, with a multi-strand core protected by an abrasion-resistant woven sheath. For most applications, low-stretch rope (typically ~2% stretch when under the load of a typical bodyweight) called static rope is used to reduce bouncing and to allow easier ascending of the rope.
* A harness is used around the waist to secure the descender. A comfortable harness is important for descents that may take many hours.
* A descender or rappel device is a friction device or friction hitch that allows for rope to be paid out in a controlled fashion, under load, with a minimal effort by the person controlling it. The speed at which the rappeller descends is controlled by applying greater or lesser force on the rope below the device or altering the angle at which the rope exits the device. Descenders can be task-designed or improvised from other equipment:
o Mechanical descenders include braking bars, the figure eight, the abseil rack, the "bobbin" (and its self-locking variant the "stop"), the gold tail, and the "sky genie" used by some window-washers and wildfire firefighters.
o Some improvised descenders include the Munter hitch, a carabiner wrap, the basic crossed-carabiner brake and the piton bar brake (sometimes called the carabiner and piton). There is an older, more uncomfortable, method of wrapping the rope around one's body for friction, as in the Dulfersitz or Geneva methods used by climbers in the 1960s.

Application

Abseiling is used in a number of applications, including:

* Rock climbers returning to the base of a climb or to a point where they then try a new route.
* Recreational abseilers, who return to the top of the line by track, stairs or other methods and abseil again.
* Recreational canyoners, who travel down mountainous watercourses where waterfalls or cliffs may need to be descended and simply jumping is too dangerous or impossible.
* Recreational caving, where underground pitches are accessed using this method (Single Rope Technique).
* Adventure racers, whose events often including abseiling and other rope work.
* Industrial/Commercial workers, who use abseiling techniques to access parts of structures or buildings so as to perform maintenance, cleaning or construction. (eg window cleaners, railway scalers, quarry workers, etc.)
* Access to wildfires or wilderness rescue/paramedic operations by rapelling from a hovering helicopter.
* Confined spaces access, such as investigating ballast tanks and other areas of ships.
* Rescue applications, such as accessing injured people or accident sites (vehicle or aircraft) and extracting the casualty using abseiling techniques.
* Steeplejacking, as a replacement for bosun's chair.
* Military and police applications, such as entering a building through a window or hard to reach spaces via aircraft. This is a technique used by special forces and SWAT teams.

Abseiling can be a dangerous sport, and presents risks, especially to unsupervised or inexperienced climbers. Abseiling is, in fact, viewed by climbers as being more dangerous than climbing itself, as the rope system is taking the weight of the practitioner constantly rather than only in the event of a fall. Moreover, a high percentage of mishaps classified as "climbing accidents" actually occur when abseiling.

Abseiling is prohibited or discouraged in some areas, due to the potential for rock erosion and/or conflict with climbers heading upwards.