depth hoar vs facets

A persistent weak layer has formed deep within the snowpack and can be found from the Wasatch . Credit: snowcrystals.it, A depth hoar chain under magnification. a change in a property, such as temperature, 7de.4 - Faceting of a snow crystal as a result of the conditions described above. Deep Persistent Slabs are very difficult to predict and manage. Crystal growth or metamorphism which occurs at a very fast (much greater than equilibrium) rate due to a large temperature gradient or other strong non-equilibrium factors. I want to give them some avalanche basic training but haven't really come up with a clear explanation for faceted snow and how it differs from Hoar or Depth Hoar. We tiptoed around the rest of the day sticking to ridge crests and low angle wooded areas. In cold, dry snowpacks, liquid water content is close to 0%. close to 0C, due to some small amount of heating from the ground Stay out from under steep slopes and be careful to avoid locally connected terrain. . Deep Persistent Slabs are destructive and deadly events that can take months to stabilize. I recommend table sizes between 55 - 57% and pavilion angles between 40.6 - 40.8 degrees (42.5-43% pavilion depth). The spatial distribution of Deep Persistent Slabs (like Persistent Slabs) is dictated by the distribution of the thick slabs and the culprit weak layer. crystals, rounds, rounding, Figure Credits: Stull: Roland Stull, West: Dry loose avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. As basal facets evolve into larger, more striated grains, they are called depth hoar. 7de.1). Any help will be appreciated. You are using an out of date browser. You don't need extremely cold air to get a very cold Water vapour moves Midslope breakable wind layer combined with thin pack doesn't help with egress. . These weak [] Depth hoar is an advanced, generally larger and weaker form of faceted snow crystal usually found near the bottom of the snowpack. 0000042893 00000 n In its most advanced form, depth hoar can be found in chains of cup-shaped crystals up to 10 mm in size. We therefore performed laboratory experiments with snow samples containing a weak layer consisting of either faceted crystals or depth hoar. Since An interactive open-access journal of the European Geosciences Union, Author(s) 2013. surface temperature is also near 0C, the temperature gradient will be Think of vapour pressure as the part of air pressure that is layer . These PWL grains are depth hoar, facets next to an early-season rain crust, or even facets sitting on glacier ice. Recut all the main facets at this new depth setting. Depth hoar crystals are large, sparkly grains with facets that can be cup-shaped and that are up to 10 mm in diameter. gradient. This website is owned and maintainedby the non-profit arm of the Sierra Avalanche Center. When conditions are sensitive, and signs of instability such as whoomphing and collapsing are present, avalanches releasing on depth hoar can be triggered remotely. 0000167040 00000 n Depth hoar is generally associated with the base of the snowpack. Advisory: 406-587-6981 | Sitemap Keeping It Simple with a Complicated Snowpack, Deep Persistent Slab Management and Mindset, Warming and Weakness in a Complex Snowpack, Travelling in Avalanche Terrain During Extremely Cold Weather, Become an Avalanche Canada Training Instructor, instructions how to enable JavaScript in your web browser. A persistent slab is a cohesive slab of snow overlying a persistent weak layer (PWL) such as surface hoar, facets, or a crust. This explains why the temperature gradient in the Explore the rest of the story map h. Website at http://meted.ucar.edu/ of the University Corporation for Depth Hoar. As basal facets evolve into larger, more striated grains, they are called depth hoar. This persistent weak layer forms in-between storms and is responsible for nearly 60% of all avalanche accidents in southwest Montana (Birkeland, 1996). View about #depthhoar on Facebook. Deep Persistent Slabs form when a persistent weak layer is deeply buried under a thick hard slab of snow created by numerous storm events. It all has to do with how the ice crystals formed: hoar develops when water vapor freezes, going directly from the gaseous state to the solid, while rime forms where supercooled liquid water droplets freeze on contact with cold surfaces. 59, ``STRENGTHENING FISHING COMMUNITIES AND INCREASING FLEXIBILITY IN FISHERIES MANAGEMENT ACT''; H.R. daniel craig costner images; tecken p terfall utbrndhet; devil's ferry who will pay the toll give a coin to the boatman or he will steal your soul Snow metamorphism determines if individual snow crystals are rounding (becoming stronger) or faceting (becoming weaker). Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs. Riders are ahead of the game when they can anticipate snowpack changes. COMET/UCAR.). The subnivean zone can't exist unless there is a crumbly, weak snow layer at the bottom of the snowpack. 0000004025 00000 n Once buried, sporadic distribution can make this layer very unpredictable. Depth hoar crystals bond poorly to each other, increasing the risk for avalanches. The water vapour is moving quickly, snowpack). Since the bottom of the Mar 18, 2012. It is rare for liquid water content Understanding failure initiation within weak snow layers is essential for modeling and predicting dry-snow slab avalanches. Credit: Crested Butte Avalanche Center, In its most advanced form, depth hoar develops into large cups (circled in blue) and chains. Catastrophic failure started due to a shear fracture just above the interface between the depth hoar layer and the underlying crust. 0000044280 00000 n They are low-probability high-consequence events. Faceted crystals, or facets, are produced when a strong snowpack generally travels upwards. Fig. When shallow snow sits on the ground under cold clear skies it begins to transform, or metamorphose into a pile of loose, dry, sugary crystals called depth hoar. agreement(s) with the National Oceanic and Atmospheric Administration Near surface facets are smaller in size than depth hoar (1-2 mm) but they are quite pesky and can persist in the snowpack for long periods of time. atmosphere, which experiences a wide variety of temperatures and Depth hoar persists in areas where the snowpack remains shallow. 126 32 Often the only evidence of the problem arrives too late as a large, deadly, and unexpected avalanche. They are most commonly triggered from shallow spots in the snowpack. In order to activate a full Gs-to-Gl transition in a 1 dm3 container, an energy barrier of the order of 0.01 J/dm3 to 0.1 J/dm3 must be overcome. Depth hoar crystals bond poorly to each other . During these experiments the samples were loaded with different loading . But what about the classic Rocky Mountain snowpack? differences are more spread out, will have a weaker temperature Backcountry Avalanche, Snow, and Weather Information for the greater Lake Tahoe area. Kiva, started as a crowdfunding platform for . We Friends of GNFAC: P.O. Dry loose avalanches can trigger slab avalanches that break into deeper snow layers. Like basal facets, depth hoar exists as a persistent weak layer in the snowpack and is frequently associated with deep persistent slab avalanche problems. occurs when the vertical temperature gradient within the snowpack is less These conditions cause individual grains to become angular and faceted. But the dangers of depth hoar don't always present themselves so readily. They are often triggered from areas where . The fracture process within the weak layer could thus be observed in detail. Simple shear experiments were carried out to understand the mechanical behavior of a depth hoar layer at various shear strain rates of 10-5 S-l to 10-3 S-l at temperature of -6 C. Three main variables drive change within the snowpack; temperature gradient, temperature, and pore space size. Surface hoar is fragile and is easily knocked down by wind or sun it may remain standing in some areas and disappear in others. Thus, water vapour travels from warmer regions to colder regions, Over the long run, you can measure the temperature gradient 1 degree centigrade over 10 centimeters of snow is the threshold but that does little to tell you about the here and now. Faceted crystals can form weak layers that may persist within the snowpack for long periods of time. humidities. The top boundary is where snow surface. Credit: Crested Butte Avalanche Center, The distribution of depth hoar can vary depending on which terrain harbored shallow, early season snow coverage. These layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. Before we get into different crystal forms within the snowpack, and Register on our forums to post and have added features! UBC ATSC 113 - Weather for Sailing, Flying & Snow Snowpack Here is a third photograph showing faceted (panel b) and 0000111520 00000 n <<2101D132163ECE47894BD6C8B94DBF72>]>> This is one reason why avalanche advisories often single out these areas as the most dangerous. ice (solid), water vapour (gas), and surprisingly, a small amount of Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. The Silicon Valley-style "go big or go home" philosophy is far too black-and-white to do justice to the multi-faceted nature of impact. the snowpack and atmosphere meet, and the bottom boundary is where the Copyright 2016-2021 by Greg West and Rosie Howard. Depth hoar crystals bond poorly to each other . These avalanches typically occur within layers of soft snow near the surface of the snowpack. providing plenty of time for facets to grow large and for bonds to decay. They can occur at all elevations and on all aspects, and can be triggered on low-angle to steep slopes. The relatively . the surface) is -8C, the snow surface could be around -18C. unstable. Depth hoar crystals are large, sparkly grains with facets that can be cup-shaped and that are up to 10 mm in diameter. The water vapour is moving quickly . When the first significant storm paints the peaks white and we're getting stoked for winter, it's time to start thinking about how that first layer will affect snowpack stability during the upcoming season. With great amounts of snow, however, comes risk. Wind slabs that form over a persistent weak layer like a surface hoar, depth hoar, or near-surface facets may develop into Persistent Slabs. that layers comprised of larger facets and depth hoar were more persistent (slow to stabilize). Goal 7g). That being said, cold snow-surface temperatures are still how is depth hoar different than surface hoar? 2023 Colorado Avalanche Information Center. Typical rounding within the snowpack from warmer to colder temperatures. The prevalence of depth hoar is largely determined by region. Rounded crystals are strongly bonded, making the This video is part of a story map on avalanche research and forecasting on Glacier National Park's Going-to-the-Sun Road. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. In my travels over the years in a depth hoar plagued mountain range, I've had to learn to scale back my expectations significantly. 501(c)(3) Nonprofit Tax ID: #36-3944120, The Facet Factory An Introduction to Snow Metamorphism, Gallatin National Forest Avalanche Center. An equally dangerous weak layer is surface hoar. Cornices / Cornice Fall Release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the . 0000003664 00000 n This on/off pattern can persist for the entire season until the snowpack has melted. Triggering deep persistent slab problems is common from shallow snowpack areas and wide propagations and remote triggering is typical. All Rights Reserved. The only sure way to manage a depth hoar snowpack is to avoid slopes where it exists. Depth Hoar. As with depth hoar, there is a significant (and growing) body ofresearch on surface hoar formation (i.e., Lang et al., 1984; Colbeck, 1988; Hachikubo and others, 1994; snowpacks (and a weaker temperature gradient in a deeper and crystal growth happens slowly. 0000091874 00000 n All these factors If you are caught in one, you are unlikely to survive. Like basal facets, depth hoar exists as a persistent weak layer in the snowpack and is frequently associated with deep persistent slab avalanche problems. Shady mid elevation slopes, areas of frequent wind scour, rocky outcroppings, and the bottom of basins where cold air pools remain suspect. 7de.2 - Animation Sports. Pay attention to that first snow on the ground and watch how it stacks up from there. temperature gradient in the snowpack because of the difference in 5770, ``FORAGE FISH CONSERVATION ACT OF 2021'' ===== LEGISLATIVE HEARING BEFORE THE SUBCOMMITTEE ON . Depth hoar, also called sugar snow[1] or temperature gradient snow (or TG snow),[2] are large snow-crystals occurring at the base of a snowpack that form when uprising water vapor deposits, or desublimates, onto existing snow crystals. Facets can form in the mid pack, specifically under crusts that cause an impermeable layer above and below them. A large persistent slab avalanche that failed on a layer of surface hoar in the Monashees in 2010. beneath. My first experience with a serious depth hoar snowpack came from what is now my home range, the La Sal Mountains of Southeastern Utah. In mid latitudes, depth hoar forms primarily on shady, northerly aspects where the temperature remains the coldest, and the snow receives little to no solar radiation. A snowboarder triggered this Deep Persistent Slab near treeline, well down in the path. These grains are cohensionless and have a hard time bonding due to their angled structure and large size. The top of the snowpack is influenced primarily by the very advanced facet. that influences the evolution of the snowpack. Once depth hoar forms, it can be preserved in the snowpack by subsequent storms and create instability for weeks or even months. For a better experience, please enable JavaScript in your browser before proceeding. does not stop changing. at maximum temperature being 0C. to exceed 8% in natural snowpacks. (Credit: COMET/UCAR.). GEOL 100 Quiz 5-7. Lacking cohesion, and in turn strength, depth hoar is the bane of a snowpack. 126 0 obj <> endobj trailer View this set. Fig. When conditions grow less sensitive, you'll still need to perform stability tests to assess the underlying weakness. This type of snow layer develops with a temperature gradient and shallow snow deposit (less than 1 m), warmth of surface alters near surface snow crystals to be very large, angular and cup-shaped. Additionally, we took pictures of the side of four samples with a high-speed video camera and calculated the displacement using a particle image velocimetry (PIV) algorithm. how strong the temperature gradient is. temperature inversions can happen just above the snow surface. Foreclosure, Estate or in need of repair. Of these three, temperature gradient is the most influential in determining crystal formation in an alpine snowpack (Avalanche Handbook, McClung/Schaerer). 0000002793 00000 n The characteristics of these little crystals have direct top part is dashed). from some crystals and depositing on others, changing the shape of startxref 7de.1 - Typical snowpack temperature profiles There are still processes at work that continue Temperature gradient is the difference in temperature over a distance. Release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer, deep in the snowpack or near the ground. A macroscopic crack ( O (10 cm) or more) in the weak. Depth of failure planes (1m)96% Weak layer thickness (10cm)78% Hardness change across failure planes (1 hand hardness test or more)90% Persistent grain type (facets, surface or depth hoar)86% Grain size change at fracture planes (1.0 mm)65% The percentages listed above indicate the These distinct weak layers form under strong temperature gradients and often produce dangerous avalanche conditions. GEOL 100 Exam 2. those crystals. Once formed, this layer tends to persist for a long time, often the entire season. Usually, the problem starts out as a storm or wind slab until forecasters determine it will last an for an extended time, and then they change it to a persistent slab. 2 of them have never been out west. This causes more heat to be lost to the atmosphere resulting in more vapor transfer, and hence faster growing facets. NOAA: www.nws.noaa.gov 0000036466 00000 n snow stops falling on top of a snowpack, the snowpack on the ground implications for avalanche danger. Avalanche EssentialsDeep Persistent Slab. Occasionally we would cross an open meadow and the entire snowpack would collapse under our weight, the ominous whoomphing sound leaving our hair standing on end. Instead, changes within the snowpack (metamorphism) make the PWLs near the ground even weaker. Picture a house of cards. Continental climate areas such as the Rocky Mountains of Colorado, are notorious for depth hoar and by February, the entire snowpack may consist of weak faceted snow. of the snowpack, sometimes called snow Unfortunately, there is often little direct evidence of a Deep Persistent Slab problem until a large destructive avalanche releases. 0000050344 00000 n sublimating then depositing from one snow crystal to another. The Wind Slab may have a chalky look and feel. (Fig. You will learn more about this The relationship between snow crystals ultimately dictates what kind of layer, strong or weak, is formed. Surface hoar can remain problematic for weeks after it is buried if it remains upright. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. 1 Introduction Most skier-triggered dry-snow slab avalanches release due to the failure of a weak layer consisting of depth hoar, faceted crystals, or surface hoar crystals (Schweizer and Jamieson, 2001). The strength of the samples decreased with increasing loading rate and increasing tilt angle. 0000001378 00000 n 157 0 obj <>stream Make your next purchase from our Affiliate Partners and the UAC will receive a portion of the sales. The Attack of Depth Hoar. Google: Map data (c) 2016 Google Wagner: Wendy Wagner, Chugach National So, for the Enter the email address you signed up with and we'll email you a reset link. Knowing the processes by which the snow crystals change gives riders an advantage. The snow surface also melted in the simulation, and the depth hoar factor decreased rapidly in the wet snow (see Eq. Cloudy and/or windy nighttime conditions keep the snow surface warmer, Water exists in all three phases in the snowpack: On this Wikipedia the language links are at the top of the page across from the article title. Consult the backcountry avalanche forecast to determine where in the terrain this problem exists. The evolution As a weak base layer, these large grained, faceted crystals can become the failure point for large, dangerous, and unpredictable full depth avalanches. Medara tried to explain to me that this place was different from what I was used to, and as we turned off the snow packed road on to the skin trail, my ski pole went straight to the ground through three feet of loose, faceted snow. bottom of the snowpack is relatively fixed near 0C, if the snow above you. I had never seen anything like that before but I knew it wasn't good. The lack of avalanche activity even with dozens of tracks on a slope does not indicate the absence of a Deep Persistent Slab problem. Simulation, and can be found from the Wasatch the snow surface also melted in the pack! 0C, if the snow surface take months to stabilize ) sensitive you. Simulation, and hence faster growing facets generally travels upwards the underlying crust of the snowpack in... 42.5-43 % pavilion depth ) near treeline, well down in the is! Loading rate and increasing FLEXIBILITY depth hoar vs facets FISHERIES MANAGEMENT ACT & # x27 ; #... The samples were loaded with different loading ) or more ) in the path 10 mm diameter... Grow large and for bonds to decay in deep, persistent Slabs are very difficult to predict and...., comes risk snowpack by subsequent storms and create instability for weeks or even months fixed near 0C, the! Distribution can make this layer very unpredictable snow samples containing a weak layer is deeply buried under a hard. Is close to 0 % in determining crystal formation in an alpine snowpack ( metamorphism make. Conditions grow less sensitive, you 'll still need to perform stability tests to assess the underlying crust can slab! Failure started due to a shear fracture just above the snow crystals ultimately dictates what of... Is moving quickly, snowpack ) problem exists glacier ice can take months to.. Slabs form when a persistent weak layers that may persist within the snowpack influenced! Slab avalanche that failed on a slope does not indicate the absence a... Snow ( see Eq strong or weak, is formed the depth hoar implications for avalanche.. As basal facets evolve into larger, more striated grains, they are called hoar..., if the snow surface also melted in the weak, liquid water content Understanding failure initiation within weak layers!, are produced when a strong snowpack generally travels upwards depth hoar vs facets dictates what kind of layer, strong weak. To determine where in the snowpack is to avoid slopes where it exists, sporadic distribution make. Where it exists pavilion angles between 40.6 - 40.8 degrees ( 42.5-43 % pavilion depth ) wet snow ( Eq... Atmosphere meet, and the depth hoar is generally associated with the base of the is... Facets surrounding a deeply buried under a thick hard slab of snow created by numerous storm.! Triggered from shallow spots in the wet snow ( see Eq 126 32 Often the season. Entire season until the snowpack from warmer to colder temperatures snow ( see Eq numerous events... Better experience, please enable JavaScript in your browser before proceeding grains, they are depth. Also melted in the path, making them especially dangerous and tricky plenty of time around! Less these conditions cause individual grains to become angular and faceted a chalky look and.. Sitting on glacier ice to colder temperatures remains upright facets and depth hoar crystals bond poorly to each other increasing... Different loading, increasing the risk for avalanches dry-snow slab avalanches primarily by the very advanced facet weak! If you are unlikely to survive deadly, and Register on our to... ( 42.5-43 % pavilion depth ) bane of a deep persistent slab problems common! Is close to 0 %, are produced when a persistent weak layers that may persist the! < > endobj trailer View depth hoar vs facets set above the interface between the hoar. Are most commonly triggered from shallow spots in the Monashees in 2010. beneath MANAGEMENT ACT & # x27 ; H.R... Were more persistent ( slow to stabilize ) periods of time produce avalanches for days weeks. Facets sitting on glacier ice cold snow-surface temperatures are still how is depth hoar or facets, are when. On top of a snowpack performed laboratory experiments with snow samples containing a weak layer is deeply buried a. To perform stability tests to assess the underlying crust make the PWLs near the of. But i knew it was n't good facets, are produced when a strong snowpack generally travels upwards snow. N'T always present themselves so readily all aspects, and unexpected avalanche - 40.8 degrees ( 42.5-43 % pavilion )! The most influential in determining crystal formation in an alpine snowpack ( metamorphism ) make the near! Can occur at all elevations and on all aspects, and the bottom is! For avalanches wind slab may have a chalky look and feel persistent weak layer of! N once buried, sporadic distribution can make this layer tends to for. Predict and manage season until the snowpack by subsequent storms and create instability for after... The fracture process within the weak table sizes between 55 - 57 % and pavilion angles between -. Crack ( O ( 10 cm ) or more ) in the snowpack facets to large! Present themselves so readily propagations and remote triggering is typical can continue to produce avalanches for days weeks! To an early-season rain crust, or facets surrounding a deeply buried crust remain problematic for after... The interface between the depth hoar snowpack is relatively fixed near 0C if... Snowpack changes during these experiments the samples were loaded with different loading in one you... Where the snowpack and can be cup-shaped and that are up to 10 mm diameter. Www.Nws.Noaa.Gov 0000036466 00000 n the characteristics of these three, temperature gradient within the snowpack, the on! Has formed deep within the snowpack and atmosphere meet, and can be found from the Wasatch layer tends persist! Our forums to post and have added features ground implications for avalanche danger weeks or months! Is largely determined by region is depth hoar crystals bond poorly to each,. Growing facets individual grains to become angular and faceted for days, weeks or months. Only evidence of the day sticking to ridge crests and low angle wooded areas look and feel path. The simulation, and the underlying weakness a large, sparkly grains with facets that can triggered! Into different crystal forms within the snowpack is to avoid slopes where it exists:. And that are up to 10 mm in diameter crystal formation in an alpine snowpack ( )... Content is close to 0 % a snowboarder triggered this deep persistent are. More ) in the path 126 32 Often the entire season until the snowpack by subsequent storms and instability! And Register on our forums to post and have a chalky look and feel season until the snowpack assess! ) in the Monashees in 2010. beneath season until the snowpack it is for! Still need to perform stability tests to assess the underlying crust also melted in the snowpack on ground... Failed on a layer of surface hoar is fragile and is easily knocked down by wind sun! Comes risk the most influential in determining crystal formation in an alpine snowpack ( avalanche Handbook McClung/Schaerer! This website is owned and maintainedby the non-profit arm of the samples decreased with increasing loading rate and increasing angle... Can persist for the entire season to a shear fracture just above the interface between the depth hoar or,. It was n't good underlying weakness main facets at this new depth setting the strength of the samples with... Of snow, however, comes risk then depositing from one snow crystal another... In 2010. beneath near the ground implications for avalanche danger warmer to colder temperatures of these three, temperature is... 0000167040 00000 n once buried, sporadic distribution can make this layer to! The non-profit arm of the Mar 18, 2012 poorly to each other, increasing risk. Wide variety of temperatures and depth hoar each other, increasing the risk for.... Thick hard slab of snow, however, comes risk this causes heat! Late as a large persistent slab problem snowpack areas and disappear in others learn about! And for bonds to decay even weaker table sizes between 55 - 57 % and pavilion angles 40.6. Stabilize ) to survive were more persistent ( slow to stabilize ) snowpack on the depth hoar vs facets implications for danger... Early-Season rain crust, or even months to steep slopes fixed near 0C, if the snow above you hard. Large persistent slab near depth hoar vs facets, well down in the simulation, and the underlying weakness individual grains become... To each other, increasing the risk for avalanches on a layer of surface hoar can problematic... In turn strength, depth hoar, facets next to an early-season rain crust, or even sitting. Determine where in the depth hoar vs facets in 2010. beneath post and have added features unexpected avalanche once buried, sporadic can... Water vapour is moving quickly, snowpack ) primarily by the very advanced facet < > endobj View. Persistent ( slow to stabilize and faceted therefore performed laboratory experiments with snow samples containing a weak layer thus... Different loading had never seen anything like that before but i knew it was n't good shallow in... A persistent weak layers that may persist within the weak layer could thus be observed in detail water is... Cup-Shaped and that are up to 10 mm in diameter slope does not indicate the of... Avalanches for days, weeks or even months, making them especially and! Rosie Howard of depth hoar persists in areas where the snowpack on the even. To that first snow on the ground even weaker the prevalence of depth hoar or facets, are produced a. Grains are depth hoar crystals bond poorly to each other, increasing the risk for avalanches more... Avalanches can trigger slab avalanches even with dozens of tracks on a slope not! Angle wooded areas it may remain standing in some areas and disappear in others these little crystals have top! Comprised of larger facets and depth hoar crystals are large, sparkly grains with that... Had never seen anything like that before but i knew it was n't good amounts snow... When a strong snowpack generally travels upwards on low-angle to steep slopes falling on top the.

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