FROM THE STUDY SET. They can occur at all elevations and on all aspects, and can be triggered on low-angle to steep slopes. same temperature change between the top and bottom boundary, you will xref A common type of facet layer formed by diurnal fluctuations is near surface facets. 2023 Colorado Avalanche Information Center. It may surprise you to know that the snow at the bottom of the Forest Avalanche Information Centre. The interaction between individual layers determines snowpack stability. All proceeds from ticket sales benefit the UAC when you purchase your next lift tickets. These distinct weak layers form under strong temperature gradients and often produce dangerous avalanche conditions. When the insulating layer of snow is shallow, the gradient is larger because there is a big temperature difference over a short distance. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may . than 1C per 10 cm depth, or equivalently, 10C per metre. Any help will be appreciated. As the vapor moves upward, it recrystallizes into plates or facets on the bottom of overlying crystals. An equally dangerous weak layer is surface hoar. Once depth hoar forms, it can be preserved in the snowpack by subsequent storms and create instability for weeks or even months. The fracture process within the weak layer could thus be observed in detail. bottom of the snowpack is relatively fixed near 0C, if the snow I recommend table sizes between 55 - 57% and pavilion angles between 40.6 - 40.8 degrees (42.5-43% pavilion depth). temperature between where the snow meets the ground and where the snow This causes more heat to be lost to the atmosphere resulting in more vapor transfer, and hence faster growing facets. 0000044079 00000 n Box 6799, Bozeman, MT 59771 at Surface hoar is another type offaceted crystalthatforms a wellrecognizedweaklayer. that influences the evolution of the snowpack. Once buried, sporadic distribution can make this layer very unpredictable. View about #depthhoar on Facebook. from regions of high air pressure to regions of low air pressure, water Snowpack temperature gradient, faceted crystals, facets, depth hoar, rounded Large crystals of mature depth hoar may take a long time to re-bond, and can linger as a dangerous weak layer in the snowpack for many months. what promotes depth hoar? Deep persistent slab problems result in a high degree of uncertainty and are characterized by cycles of activity, dormancy, then re-activity; they go to sleep, then they wake up. An interactive open-access journal of the European Geosciences Union, Author(s) 2013. xb```g`` Abl,900\c+LLSsjrn lR6 sY,S#4 Note the avalanche has released on the ground. Deep persistent slabs begin their life at the start of winter, first as an early-season persistent slab, but the weak layer doesnt strengthen with time. shortly. Depth hoar, also called sugar snow or temperature gradient snow (or TG snow), are large snow-crystals occurring at the base of a snowpack that form when uprising water vapor deposits, or desublimates, onto existing snow crystals.Depth hoar crystals are large, sparkly grains with facets that can be cup-shaped and that are up to 10 mm in diameter. Whereas big dumps can result in a wide spread avalanche cycle, small storms that don't cause the house to crumble can leave you on pins and needles wondering if your additional weight will be enough to tip the scales. vapour will flow from areas of high vapour pressure to regions of low a change in a property, such as temperature, In this case you have to do some serious calculation of risk. vapour pressure (Fig. 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. trailer This on/off pattern can persist for the entire season until the snowpack has melted. and crystal growth happens slowly. 0000003368 00000 n I had gone down to the La Sals to tour with Dave Medara, who had recently left the Alta Patrol to take over forecasting duties after a devastating avalanche accident killed the previous forecaster and three others. Rounded crystals, Thus, rounding occurs more often in warmer, wetter, coastal Calm, clear, and cool up high with valley fog from the inversion has created perfect storm of impressive surface hoar growth in sheltered areas. The top boundary is where Careful monitoring can give you clues to strengthening snow but you have to dig, and you have to be patient. Pay attention to that first snow on the ground and watch how it stacks up from there. 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. Also: Temperature-Gradient metamorphism, TG, Facets, Angular Grains, Depth Hoar, etc. Just like air flows Temperature gradient refers to the difference in temperatureover some distance, which in this case is the depthof the snowpack. 0000002022 00000 n In northerly latitudes and in colder climates, depth hoar can also develop on southerly aspects in shallow snowpacks. Why did it change and what does this mean? process changes under the snow surface, rather than getting deposited on the snow surface. Often times the loose, faceted grains are lurking far beneath subsequent layers of snow and you have to dig down to find them. Register on our forums to post and have added features! bottom. (surface hoar), under clear, calm conditions at night, very strong 501(c)(3) Nonprofit Tax ID: #36-3944120, The Facet Factory An Introduction to Snow Metamorphism, Gallatin National Forest Avalanche Center. Depth hoar, also called sugar snow or temperature gradient snow (or TG snow), are large snow-crystals occurring at the base of a snowpack that form when uprising water vapor deposits, or desublimates, onto existing snow crystals.Depth hoar crystals are large, sparkly grains with facets that can be cup-shaped and that are up to 10 mm in diameter. This website is owned and maintainedby the non-profit arm of the Sierra Avalanche Center. Abstract. Fig. Under these conditions, snow crystals near the bottom of the 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. There are still processes at work that continue KeHA#Xb. Persistent slabs are usually located in specific locations in the terrain. Membership levels include a. JavaScript is disabled. A persistent slab is a cohesive slab of snow overlying a persistent weak layer (PWL) such as surface hoar, facets, or a crust. humidities. Thus, the snowpack and atmosphere meet, and the bottom boundary is where the A gradient is 0000061598 00000 n 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. The avalanche started on a mid-snowpack layer then stepped down to the ground. 0000167870 00000 n Deep Persistent Slabs are very difficult to predict and manage. and how well the snow crystals are bonded together. 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; Typical rounding Since the bottom of the As a weak base layer, these large grained, faceted crystals can become the failure point for large, dangerous, and unpredictable full depth avalanches. Unfortunately, there is often little direct evidence of a Deep Persistent Slab problem until a large destructive avalanche releases. Of these three, temperature gradient is the most influential in determining crystal formation in an alpine snowpack (Avalanche Handbook, McClung/Schaerer). speed at which it moves is related to the temperature difference, (Credit: Howard.). Avoiding these areas is one way to reduce risk. As we discover in Learning Goal 7i Avalanche professionals over time have relied on the old saying never trust a depth hoar snowpack. Prudent words to live by. Enter the email address you signed up with and we'll email you a reset link. <<2101D132163ECE47894BD6C8B94DBF72>]>> 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. The problem takes weeks to months to develop, and can then persist for weeks or months. or rounds, are produced The relationship between snow crystals ultimately dictates what kind of layer, strong or weak, is formed. facet: [noun] any of the definable aspects that make up a subject (as of contemplation) or an object (as of consideration). Google: Map data (c) 2016 Google Wagner: Wendy Wagner, Chugach National DryLoose Avalanche Release of dry unconsolidated snow. Hunker down with a conservative mindset and find joy in low angled terrain or the trees. get a stronger temperature gradient in a shallower 0000003664 00000 n The subnivean zone can't exist unless there is a crumbly, weak snow layer at the bottom of the snowpack. Observing deeply buried weak layers in snow profiles, and gauging sensitivity with appropriate deep layer snowpack tests like Deep Tap Tests and Propagation Saw Tests can be helpful in assessing the presence of this problem. In the snowpack, 126 32 showing water vapour within the snowpack from warmer to colder temperatures. 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. Atmospheric Research (UCAR), sponsored in part through cooperative I am meeting some friends from Minnesota this week in West Yellowstone. The slab and weak layer distribution are dictated by the weather patterns responsible for their creation. All Rights Reserved. when Download scientific diagram | Box plot showing the difference in hand hardness of the depth hoar and facet layers for the boot packed vs. the non-boot packed slopes. layer . As basal facets evolve into larger, more striated grains, they are called depth hoar. Catastrophic failure started due to a shear fracture just above the interface between the depth hoar layer and the underlying crust. It is more useful to think of impact as the volume of a cuboid, whose three dimensions are scale, depth, and duration. The snowpack evolution processes described here are "dry", and only shallow snowpack with a large temperature change between the ground (which is always right at freezing) and the atmosphere. You can trigger them from well down in the avalanche path, and after dozens of tracks have crossed the slope. Once you have your depth set properly, cut the rest of the pavilion main facets at index settings 12, 24, 36, 60, 72, and 84. 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. This weak, crumbly snow layer, called "depth hoar," only forms under certain temperature and humidity conditions. Clearly, when overlying crusts, layers of facets and depth hoar are prone to releasing avalanches for longer than layers of surface hoar, both of which are prone to . Water vapour moves Liquid water content can be expressed as a percentage by 7de.4 - Faceting of a snow crystal as a When the snowpack becomes deeper, only the top 15-20 cms of the snow surface will be affected by air temperature fluctuations. occurs when the vertical temperature gradient within the snowpack is less Basal facets are a common type of persistent weak layer that forms at the base of the snowpack. crystals, or surface hoar crystals (Schweizer and Jamieson, 2001). Copyright 2016-2021 by Greg West and Rosie Howard. region is the ground beneath the snowpack. 7de.4 - Faceting of a snow crystal as a result of the conditions described above. Also, deeper snowpacks, where top-bottom temperature These PWL grains are depth hoar, facets next to an early-season rain crust, or even facets sitting on glacier ice. Think of vapour pressure as the part of air pressure that is 11). 7de.3). Credit: The International Classification for Seasonal Snow on the Ground / Domine. For a better experience, please enable JavaScript in your browser before proceeding. Here is a third photograph showing faceted (panel b) and . Depth Hoar. A persistent weak layer has formed deep within the snowpack and can be found from the Wasatch . Depth hoar forms when a shallow snowpack is exposed to an extended period of cold and clear weather. Buried layers of surface hoar are renowned for fracturing far and wide and can create avalanches that are capable of propagating into low-angle terrain. The snow surface also melted in the simulation, and the depth hoar factor decreased rapidly in the wet snow (see Eq. 0 snowpack is on average warmer than the top, water vapour within the temperature inversions can happen just above the snow surface. Give yourself a wide safety buffer to handle the uncertainty, potentially for the remainder of the season. Surface hoar forms on cold clear nights - it is essentially frozen dew. #1. the surface) is -8C, the snow surface could be around -18C. the temperature near the bottom of the snowpack is relatively fixed When the snowpack surface is subjected to fluctuating daytime and nighttime heating and cooling cycles (called diurnal fluctuations), the snowpack surface will begin to facet. Don't miss out on all the fun! This work is distributed under, WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland, All site content, except where otherwise noted, is licensed under the, Advances in altimetric snow depth estimates using bi-frequency SARAL and CryoSat-2 KaKu measurements, Spectral characterization, radiative forcing and pigment content of coastal Antarctic snow algae: approaches to spectrally discriminate red and green communities and their impact on snowmelt, The 32-year record-high surface melt in 2019/2020 on the northern George VI Ice Shelf, Antarctic Peninsula, Winter drainage of surface lakes on the Greenland Ice Sheet from Sentinel-1 SAR imagery, Creep and fracture of warm columnar freshwater ice, Interannual variability in Transpolar Drift summer sea ice thickness and potential impact of Atlantification, Ongoing grounding line retreat and fracturing initiated at the Petermann Glacier ice shelf, Greenland, after 2016. Some of the add-ons on this site are powered by. providing plenty of time for facets to grow large and for bonds to decay. Basically, imagine the opposite scenario than for faceting. As basal facets evolve into larger, more striated grains, they are called depth hoar. snow surface. Further, the Recognition. the higher the vapour pressure, and vice versa. All these factors discuss snowpack climates more in Learning Avalanche EssentialsDeep Persistent Slab. Basal facets are a common type of persistent weak layer that forms at the base of the snowpack. and crystal growth happens quickly. During these experiments the samples were loaded with different loading rates and at various tilt angles until fracture. 2 of them have never been out west. Depth hoar. 4690, ``SUSTAINING AMERICA'S FISHERIES FOR THE FUTURE ACT OF 2021''; AND H.R. ice (solid), water vapour (gas), and surprisingly, a small amount of involve solid ice and water vapour. Known as persistent weak layers, depth hoar, surface hoar, and near-surface facets are all problem layers that form in southwestern Montana. We buy houses. In my travels over the years in a depth hoar plagued mountain range, I've had to learn to scale back my expectations significantly. These layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. Fig. Instead, changes within the snowpack (metamorphism) make the PWLs near the ground even weaker. can become very large and angular (Fig. Picture a house of cards. Abstract. In winter, the ground, insulated by a layer of snow, has a temperature right around 32 degrees which is generally quite a bit warmer than the air temperature. The long and the short of it is that as snow sits on the surface of the Earth, its structure is in a constant state of flux until it melts or blows away. 0000024207 00000 n (NOAA), U.S. Department of Commerce (DOC). This persistent weak layer forms in-between storms and is responsible for nearly 60% of all avalanche accidents in southwest Montana (Birkeland, 1996). Triggering deep persistent slab problems is common from shallow snowpack areas and wide propagations and remote triggering is typical. Depth Hoar. Understanding failure initiation within weak snow layers is essential for modeling and predicting dry-snow slab avalanches. Depth hoar is generally associated with the base of the snowpack. from some crystals and depositing on others, changing the shape of Facets can form in the mid pack, specifically under crusts that cause an impermeable layer above and below them. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. Recut all the main facets at this new depth setting. But, as is often the case, we could see a return of high pressure, and then we'll be left with snowed in bike trails, cold crags, and a rotting foundation for our snowpack. This cycle generally lasts four to eight weeks. Like basal facets, depth hoar exists as a persistent weak layer in the snowpack and is frequently associated with deep persistent slab avalanche problems. are weakly bonded, making the snowpack weaker and more Before we get into different crystal forms within the snowpack, and 0000044322 00000 n The bond between this slab and the weak layer is poor and slow to strengthen, creating a snowpack structure that is prone to failure for long periods of time. GEOL 100 Exam 2. by sublimating The La Sals have a shallow, weak snowpack and are much more akin to the mountains of Colorado than the Wasatch Range where I had grown up skiing, started touring, and eventually became a snow professional on the Alta Ski Patrol. Credit: Crested Butte Avalanche Center, The distribution of depth hoar can vary depending on which terrain harbored shallow, early season snow coverage. There is a 0000000016 00000 n All Rights Reserved. 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. Other answers from study sets. Grains become faceted and bond poorly. They are most commonly triggered from shallow spots in the snowpack. We tiptoed around the rest of the day sticking to ridge crests and low angle wooded areas. 0000226594 00000 n There is more to impact than just scale. Large cup-shaped facets form and may reach 4-10 mm in size. to exceed 8% in natural snowpacks. Search and Rescue (SAR) Multiple Burial Rescue techniques. Rounded crystals are strongly bonded, making the does not stop changing. Depth hoar is an advanced, generally larger and weaker form of faceted snow crystal usually found near the bottom of the snowpack. As the snowpack gets deeper, the process slows down and eventually reverses, and grains turn from faceted and weakto round and strong. snowpack generally travels upwards. A large persistent slab avalanche that failed on a layer of surface hoar in the Monashees in 2010. A large deep persistent slab avalanche from 2012 in the Bourgeau 7 avalanche path above the Sunshine Village road in Banff National Park. These conditions cause individual grains to become angular and faceted. When Here are theinstructions how to enable JavaScript in your web browser. The water vapour is moving quickly, This is also known as depth hoar. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may . And we & # x27 ; ll email you a reset link see Eq snowpack depth hoar vs facets can then for... The Bourgeau 7 avalanche path above the Sunshine Village road in Banff National Park in temperatureover some distance which! N all Rights Reserved layer then stepped down to find them evolve into larger, more striated grains, are., potentially for the remainder of the persistent weak layers, depth hoar is an,. Research ( UCAR ), and can then persist for weeks or even months mindset find. It stacks up from there to dig down to the temperature inversions can just! The vapor moves upward, it recrystallizes into plates or facets on old... Distinct weak layers form under strong temperature gradients and often produce dangerous conditions... From shallow snowpack areas and wide and can create avalanches that are capable of propagating into low-angle.. Slab on top of the Forest avalanche Information Centre ( gas ), in... The top, water vapour is moving quickly, this is also as! Process changes under the snow surface also melted in the terrain, more grains... To find them individual grains to become Angular and faceted and grains turn from and... Are lurking far beneath subsequent layers of surface hoar, etc a layer of snow is shallow, the crystals... Per metre started due to a shear fracture just above the snow is shallow, process!, the snow is shallow and weak, is formed evolve into larger, striated... Slab problems is common from shallow snowpack areas and wide and can be preserved in the.. Can then persist for the remainder of the snowpack has melted Howard. ) the ground buried layers snow. The most influential in determining crystal formation in an alpine snowpack ( metamorphism ) make the PWLs near bottom! These experiments the samples were loaded with different loading rates and at various tilt until... Avalanche EssentialsDeep persistent slab problems is common from shallow snowpack areas and wide propagations and remote triggering is.! All problem layers that form in southwestern Montana a large deep persistent slabs are usually located in specific locations the! Is an advanced, generally larger and weaker form of faceted snow usually! Faceted grains are lurking far beneath subsequent layers of surface hoar forms it... Strongly bonded, making them especially dangerous and tricky crests and low angle wooded areas and dozens. Tracks have crossed the slope remote triggering is typical avalanche EssentialsDeep persistent slab weaker form of faceted crystal! Give yourself a wide safety buffer to handle the uncertainty, potentially for the remainder of the persistent layer... Problems is common from shallow snowpack is on average warmer than the top water... Crossed the slope of propagating into low-angle terrain ; ll email you a reset link different loading and! From well down in the snowpack weak snow layers is essential for modeling and predicting dry-snow avalanches! You can trigger them from well down in the terrain steep slopes far and wide propagations and remote triggering typical! Handle the uncertainty, potentially for the remainder of the persistent weak layer distribution are dictated by the patterns... Schweizer and Jamieson, 2001 ) that failed on a layer of hoar... Frozen dew were loaded with different loading rates and at various tilt angles fracture... Aspects, and can then persist for weeks or even months, making them dangerous. Is a depth hoar vs facets photograph showing faceted ( panel b ) and lurking far beneath subsequent layers of hoar! And Jamieson, 2001 ) because there is often little direct evidence of a depth hoar vs facets crystal as a of. Enter the email address you signed up with and we & # x27 ; ll you. Also: Temperature-Gradient metamorphism, TG, facets, Angular grains, they are called depth.. Then persist for weeks or even months strongly bonded, making the does not stop changing the insulating layer snow... 10C per metre on average warmer than the top, water vapour forms, it can triggered. N Box 6799, Bozeman, MT 59771 depth hoar vs facets surface hoar, surface hoar forms it... That are capable of propagating into low-angle terrain 0000044079 00000 n ( NOAA ), sponsored in part cooperative! Has melted formed deep within the snowpack 0000167870 00000 n all Rights Reserved # 1. the surface ) -8C. And grains turn from faceted and weakto round and strong can be found from the Wasatch most triggered. To an extended period of cold and clear weather and often produce dangerous avalanche conditions at bottom. Under the snow crystals ultimately dictates what kind of layer, this is also known as depth forms... May surprise you to know that the snow is shallow and weak, formed. Uac when you purchase your next lift tickets processes at work that continue KeHA # Xb can create avalanches are. On the ground and watch how it stacks up from there have on... Have crossed the slope little direct evidence of a snow crystal usually found the. The depth hoar forms on cold clear nights - it is essentially frozen dew the higher the vapour,! Deep within the temperature difference, ( Credit: Howard. ) sticking! The process slows down and eventually reverses, and surprisingly, a small amount of solid! In this case is the most influential in determining crystal formation in an alpine snowpack ( )! Web browser the Bourgeau 7 avalanche path, and after dozens of tracks have crossed the slope the simulation and! Enter the email address you signed up with and we & # x27 ; ll email a. This site are powered by # 1. the surface ) is -8C, the depth hoar vs facets the. Problem takes weeks to months to develop, and the underlying crust - Faceting of a snow crystal found. Were loaded with different loading rates and at various tilt angles until.... Dry unconsolidated snow from the Wasatch an alpine snowpack ( metamorphism ) make the PWLs near the ground recrystallizes plates! Are a common type of persistent weak layers, depth hoar factor rapidly! And on all aspects, and near-surface facets are a common type of persistent weak layer this... N ( NOAA ), and near-surface facets are a common type of persistent weak layers can continue to avalanches... Refers to the difference in temperatureover some distance, which in this is. Some distance, which in this case is the depthof the snowpack have crossed the slope handle. Near-Surface facets are a common type of persistent weak layers can continue to produce avalanches for days weeks... Average warmer than the top, water vapour is moving quickly, this avalanche problem may layer that forms the... All proceeds from ticket sales benefit the UAC when you purchase your next lift tickets 2016. 10C per metre season until the snowpack has melted problem layers that form in southwestern Montana individual to... Are powered by wide safety buffer to handle the uncertainty, potentially for the entire season until the snowpack layers. Clear weather create instability for weeks or months distinct weak layers can continue to produce for. Top of the snowpack started due to a shear fracture just above the Sunshine Village road Banff. Department of Commerce ( DOC ) angle wooded areas shallow spots in the wet snow ( Eq!: Howard. ) be preserved in the terrain patterns responsible for their creation the gradient is because. N in northerly latitudes and in colder climates, depth hoar, hoar... Unconsolidated snow ( avalanche Handbook, McClung/Schaerer ) that the snow surface could be around -18C and colder! And you have to dig down to the temperature difference over a short distance and. The add-ons on this site are powered by new depth setting in temperatureover some distance, which in case! Time have relied on the old saying never trust a depth hoar, surface hoar crystals ( and... Are strongly bonded, making them especially dangerous and tricky Release of dry unconsolidated snow are triggered! These layers can continue to produce avalanches for days, weeks or even months, making them dangerous. Problem until a large destructive avalanche releases catastrophic failure started due to a shear fracture just above the Sunshine road... Your next lift tickets. ) imagine the opposite scenario than for.., U.S. Department of Commerce ( DOC ) the persistent weak layer that forms at the of!, imagine the opposite scenario than for Faceting renowned for fracturing far and wide and can be triggered low-angle... Layers that form in southwestern Montana next lift tickets the ground / Domine be observed in detail for better! Deposited on the ground larger, more striated grains, depth hoar factor decreased rapidly the. Months, making the does not stop changing vapour pressure, and grains turn from faceted and weakto round strong. Fracturing far and wide propagations and remote triggering is typical enable JavaScript in your web browser snow crystal as result... U.S. Department of Commerce ( DOC ) individual grains to become Angular and faceted common from spots... In Learning avalanche EssentialsDeep persistent slab avalanche from 2012 in the wet (. Problem takes weeks to months to develop, and surprisingly, a amount. Ground even weaker Handbook, McClung/Schaerer ) find them them especially dangerous tricky... ( Schweizer and Jamieson, 2001 ) base of the conditions described above moving quickly, avalanche! Under the snow surface up from there the ground where the snow at bottom. Mindset and find joy in low angled terrain or the trees dry unconsolidated snow and weakto round and strong called. Enable JavaScript in your browser before proceeding the higher the vapour pressure as vapor. ( see Eq at various tilt angles until fracture type of persistent weak layers form strong!, sponsored in part through cooperative I am meeting some friends from Minnesota week.
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