Howdy everyone and thank you for continuing on with module 12. In this video, we're going to talk about the different types of mass wasting. Mass movements are classified by the type of material involved and how that material moves. Earth materials can fail in a variety of ways such as flowing, sliding, falling, and subsiding, which we will talk about each in more detail shortly. Here's a chart that nicely summarizes some of the different types of mass movements. Slides are when material moves as a fairly coherent mass on a well- definfined basil surface as slump blocks or translational slides. Falls are when material free falls in air and this most commonly occurs as rock falls but soil falls can also occur. Flows which happen to be the most destructive are when when materials move as a viscous fluid and is commonly unconsolidated and water saturated. They occur as very slowm moving rock and soil creep, but can progressively get faster as earth flows, debris flows, mud flows, and debris avalanches. Here's a figure showing the different ways the earth can fail. Falls are free falling rock or soil where the dominant movement is vertically downward. Rock falls move as separate blocks as shown here. Flows literally will flow over the landscape and move as a very viscous fluid with turbulence generated within the moving mass. Slides, you guessed it, slide over top of a slip surface that can be flat or curved. These move more or less as a semi-olid mass and coherence is usually maintained within the moving mass, but not always. Subsidence occurs when material collapses or subsides into a void which we already talked about in our groundwater lecture with cars topography. This movement is mostly in the vertical downward motion and they tend to move as separate blocks as well as shown here. Let's start with rock falls. These are rapid mainly vertical free falling of rocks or less commonly blocks of soil. The videos I had saved for this lecture are not allowing me to input them into any of my slides. So, we will have to rely on photos. But I really highly recommend youtubing some of these as we move along to get a better idea on how they move and to actually see it in action. But here are two examples of rockfalls in British Columbia and the TransCanadian Highway with people for scale. Here's another rockfall near Vancouver. This one is a rockfall in Zion National Park that caused the closure of a main road back in 2015. Here's a rockfall covering an Oregon highway in 20 or 2005. Note that the rock broke free on joint surfaces where we have cracks in the rock. What acted as a weak plane and allowed this rock to fail. Rock falls are the dislodging of a rock from a steep slope as shown here on Interstate 70 along Glenwood Canyon in Colorado on the left and in Zion National Park on the right. In 1996, a 162,000 ton of granite fell from a cliff in Yusede National Park in California. We actually have a lot of spectacular images of this event. Here's an amazing photo of that rockfall in 96. And another farther out photo. Luckily, this rockfall didn't occur in a more populated part of the park, but it was still responsible for one death. The man tragically died when he was crushed not by the rockfall, but by a tree that was blown down by the air blast in front of the rockfall. Here's a photo of Glacier Point in Yusede National Park. Do you notice any planes of weaknesses in this rock? Would you really want to be standing here? It really doesn't pay to build downhill from a big rock. But where do we most often see this? In California, of course. And gravity will always win. Here are some of the aftermath of a rock fall in Malibu, California. These rocks can truly be humongous. All right, let's move to flows. Rock creep and earth flows are the slowest flows. So we will start here. The slow downs slope movement of soil or rock is known as creep. It is often the result of freezing and thawing or wetting and drying. Wetting or freezing lifts the surface particles at right angles to the slope and then the subsequent drying or thawing lowers those particles vertically causing downhill movement over time. Creep can cause fences and telephone poles to tilt. Foundations can crack and trees can curve as the ground slides or creeps out from under the tree. Here's an example of soil creep. Often times soil creep happens so slowly it goes unnoticed by us. But in places where trees are actively growing, we can see clues that the ground is indeed moving. For example, here we see curved tree trunks that preserve the movement of the land as they grow. If you ever find yourself in a place like this, you should really get out because although the land is moving slowly for now, it can suddenly fail and transition into a more rapid form of flow. Here's another example of soil creep with this fence giving us evidence of its slow movement. Rock creep can happen as well as soil creep and rock creep can slowly deform the rock layers over time like this rock layer that is being bent near Marathon, Texas. Here's rock creep and garnet shist in the black hills of South Dakota. Earth flow is similar to soil creek, but it is sped up a bit. This happens as slopes start to flow and move under gravity and usually occurs in finer grain materials that have been saturated with water. That's shown here along the side of a road. Here's another example of an earth flow in Northern California. Here's an earthflow emission pass California. Here are more earth flows. These tend to not be very deadly due to their slow movement, but they can be very costly if they occur at or near infrastructure. Here's a large scale earthflow on a hillside in central California. All right, before we get into the rapid flows, let's move on to slides first. Slides can move as slump blocks or translational slides, which move as a relatively coherent block along a more or less flat surface. Here's an example of a slide that starts out above water and moves underwater, which is common along coasts and can add additional hazards in the form of a tsunami. Here's an example of a translational slide in California at Point Ferman. California is plagued by all types of mass wasting events. Here's another translational slide at Point Ferman. All right. Debris slides occur in a similar way as translational slides. However, debris slides are when a translational slide begins to break up into many smaller blocks like this debris slide in western North Carolina. Slump blocks are rotational slides that slide along a curved surface and rotate backwards as shown here. Slumps fail along curved surfaces. This often forms a scar at the head of the slump. And at the base or toe of the slump, we find a lumpy, distorted mess. Here's a perfect example of a slump with a headscarf shown at the head and a lumpy deposit shown at the toe. Here are slump blocks blocking the Pacific Coast Highway in California. Many landslides have a headscarf and some degree of rotational slumping in the large blocks. Here's a nice figure showing all of the features that are commonly associated with landslides. Here's another one on a hillside with a prominent headscarf forming. Here's one along the coast of England. And here's a slide with rotation rotational large slump blocks, tilted trees, and even a headscarf formed at the top or the head of the slide. Okay, back to flows, but this time focusing on the faster flows, which come in the form of debris flows, mud flows, and debris avalanches. Mud flows are rapidly moving downslope slurries of water, mud, and larger debris. However, mud flows contain more than 50% water and mud. Debris flows are very similar except they contain more debris than mud with more than 50% of it consisting of larger gravel sized to even boulder sized debris but can still contain some mud. Bris avalanches are very rapidly moving downs slope masses of nearly 100% larger size debris with very little mud or water involved. Mud flows are usually the most deadly. Here is one in California. Here's another one in California. Here's a devastating mud flow in Thailand. and one in China. Here are some mud flows in Brazil that occurred in 2011. These slopes were made unstable by clear-cut logging. Humans can influence slope failure as well as nature. The mud flu in 1998 destroyed two homes in Laguna Canyon in California. Here's a mudflow in Italy. Here's a mud flow in China where I have the red arrow. You can see that the that's where the narrow canyon is where the mud flow came out of the mountains. Mud flows are often associated with volcanoes. Remember la'ar? Laar are volcanic mud flows. And here's an example of that laahar from the Mount St. Helen's 1980 eruption. Here showing some of the results of the Laahar's down river from Mount St. Helens after the eruption. A school in the Philippines was buried by a laar after Mount Pinatuba erupted in 1991. Debris flows are very similar to mud flows, but they contain more debris than mud. Here's a debris flow in Utah with a mixture of rocks from small particles to large boulders. Here's a massive debris flow deposit from the San Bernardino Mountains that covered um a huge portion of the Mojave Desert floor today. This massive debris flow, however, occurred 17,000 years ago. Here are two debris flows, and on top of them, you can see even smaller, more recent flows. Here's a chaotic deposit from a debris flow showing the varying sizes of particles that can be involved. Here's a debris flow overtaking a roadway. A mass of rock and sediment almost 1 kilometer wide and 100 meters thick buried a highway and block the Nachase River in the Cascade Mountains of Washington. Though destructive, this landslide is actually quite small compared with some that have happened in historic time. Sloping land can move and sometimes with disastrous consequences. Here's a slump block and resulting debris flow in La Konita, California. Here are photos from the 2005 Lanchita mudslide along the coast of California. In A, we can see a housing development that was built in a narrow strip between the beach and the steep cliffs. Probably not a good place to be building your home. And B, you can see that during heavy rains, the slope gave way and heavy mud flowed down, burying houses and taking several lives. At C, you can see the rescuers at the toe of the mudslide. Prior to the 2005 event, this community, La Kita in California, was subjected to an earth flow and debris flow that destroyed 12 homes in 1995. It was actually the result of heavy rains that reactivated the 1995 deposit on January 10th of 2005 that caused additional mass wasting, destroying 15 homes and killing 10 people. Another example of a debris avalanche happened in Peru in 1970 and that was triggered by an earthquake. The side of a mountain from 18,000 to 21,000 ft failed along with part of a glacier. This sent a mass of 100 million cubic meters of granite, ice, sediment, and water moving at 175 to 210 mph down the mountain, smashing into towns and burying 22,000 people in Yang and other towns. It is considered the fourth most deadliest landslide. Here's an overview of that debris avalanche. Here's a before photo of that town before the landslide, the town of Yung. And you can see the town of Yung is perched on a hill near this ice covered mountain. And here's that same view, but after the landslide. The landslide completely buried the town beneath debris. A landslide scar is visible on the mountain in the distance. You can see the debris avalanche started at the mountain and followed the topography moving around and over ridges burying everything in its path, including this town. The second most deadliest debris flow happened in Venezuela in 1999. This was one that wasn't triggered by an earthquake, but it was influenced by unseasonable storms that dumped 36 in of rain on steep mountain slopes. The vegetation here had shallow roots in the 10-ft thick soil. Cities were located at the canyon mouths where the material was funneled through as mud and debris flows traveling at 6 to 30 mph. Here's a photo of the aftermath. You can see the city is built right at the mouth of a canyon. Probably not the best place to live. This flow left a 16 ft deposit on the canyon floor. Parabaya was the hardest hit. Singlestory buildings were completely buried. Apartments were partially collapsed and 140,000 people were left homeless. It even buried a main road which impeded evacuation and rescue efforts. Poor city planning, construction standards, and building inspection exasperated the damages, costing $2 billion and killing 30,000 people. Here is another photo of the aftermath. Let's look at a somewhat recent disaster in 2014 in our very own country at Oso, Washington. A landslide on March 22nd, 2014 crossed a river and buried homes and businesses in Oso, Washington. Here's a before photo at the top and an after photo on the bottom. Take notice of the after photo. Here is the scar in the landscape, the head scar followed by the debris flow below crossing the river that was once here and homes and businesses that were built on the other side. The slide was triggered by heavy rain and it came from across the river from a slope that was unstable due to these heavy rains. Here's where the slide came down in at. And here are the homes and businesses that were impacted. Here's a photo showing the entire slide from the headscarp to the toe. You can see here it was a rotational slump that continued to break into smaller and smaller pieces as it moved down slope. Here are a few photos of the rescue and recovery efforts. 43 people were killed and that is mostly because it happened at the worst possible time on a Saturday morning when most people were at home. The slide covered over a square mile and destroyed 50 structures. Mud flows and debris flows basically turn into the consistency of concrete once the flow stops. People that are buried must be found very quickly or they will suffocate. The window to risk ris rescue anyone unfortunately closes quickly and then it becomes a recovery operation. Here's a photo of landslide debris blocking a highway. The orange marks indicate the house has been searched and whether anyone was found alive or dead. This serves as a grim reminder of the New Orleans after Hurricane Katrina. Here's a map showing other landslides in the area using a technology known as Liar. Liar is a method for determining distances by targeting an object with a laser and measuring the time for the reflected light to return to the receiver. It helps us create maps when vegetation and other material is blocking our view. Thanks to LAR, we can see that there have been many slides before OSO, all of them younger than 14,000 years, with OSO outlined in red here. So, we can't talk about mass movements without talking about avalanches. 10,000 avalanches each year in the US result in about 14 deaths annually. In the United States, they mainly occur in Rocky Mountains and the western United States, but they are also common in Europe and in the Alps. They pose a threat in mountain regions throughout the entire world. Major dangerous avalanches occur after heavy snowfall or when the warming forms a weak layer within the snow pack. Sometimes we can predict an avalanche by looking for unstable snow overhanging known as a Cornish which is shown here. Here a skier triggered an avalanche. Notice that the snow is breaking into larger flat slabs. This illustrates the zone of weaknesses within the snow pack. And these occur just like our other mass wasting events, just with snow and ice instead of soil and rock. Here's a photo of an avalanche in Sundance, Colorado in 2005. Here's one in Switzerland in 2003. Here's a remarkable one shown in Alaska. Just like debris and mud flows, people must be rescued quickly or they can suffocate. An added hazard of avalanches is that people can also die from hypothermia. Many skiers carry a beeper so they can be located if they are skiing in the back country off groom trails. Here's an aftermath of a 1999 avalanche in the Australian Alps. Masses of snow buried several homes here. You may notice that I have a love of dogs, but dogs are always vital in all sorts of rescue efforts, especially avalanche rescues. Their keen sense of smell can help rescue victims much faster. Again, time is of the essence. Avalanches can leave scars in the landscape just like our other types of mass movements. Here is an avalanche scar, also known as an avalanche shootute. This shows trees that were flattened by the avalanche and are now exposed now that the snow has melted. All right, so we already talked about subsidance in our groundwater module, but let's get into a little more detail about their hazards. Subsidance refers to the slow or rapid settling of earth materials. And these are caused by the withdrawal of water, oil, or natural gas from our subsurface reservoirs, or they can be caused by the collapse of surface material over voids, caves, or underground mines to form sink holes. Remember our example of Sanwe Valley in California. This is one example of subsidance occurring and this is due to the withdrawal of groundwater that we talked about. Subsidance in the Houston area is occurring at an alarming rate due to the withdrawal of groundwater and natural gas from beneath the city. In areas closest to the coast, we are seeing subsidance of over 10 ft. This is going to be a major problem for saltwater intrusion and for storm surge flooding. Even slight amount of subsidance under structures like this home in the UK can cause tremendous damage. This one is due to subsidance into an old underground mine. All right. And to end this video, I want to spend a little time talking about underwater landslides, which are also mass movements that happen underwater. And I happen to know a great deal about underwater landslides are tricky. They have been observed on steep nearly 50 foot vertical cliffs and nearly flat, less than one degree gradient slopes. Some are small while many are massive, moving up to 20,000 cubic km of sediment in one event. Their dynamic behavior is also variable and have the potential to create or amplify tsunami events. Landslide generated tsunamis are heavily dependent on how much and how fast sediment has moved. Some are fast, moving up to 60 m/s, while some appear to be slowly creeping like our soil creep over long periods of time. Because we cannot observe them directly, hazard assessments rely on examining the geological record, including geohysical data like the reflection data that I showed in the welcome video to help us better understand where past slope failures have occurred and where unstable areas might exist. Submarine landslides have been known to cause tsunamis that can impact coasts around the world. An example of this occurred during the 1964 Great Alaska earthquake in Resurrection Bay when a 1 kilometer long section of waterfront failed, producing a 10-meter wave that hit 30 minutes before the earthquake induced wave, killing 13 people. Sonar mapping revealed a blocky debris field with individual blocks of up to 10 to 15 m high. Here is my study area, the Cascadia margin offshore Oregon. It is considered an active margin because of the active subduction zone where the Wandafuka plate is subducting underneath the North American plate. And this produces large magnitude earthquakes about once every 600 years. The main sediment output here is coming from the rapidly eroding Cascade Mountains. And that sediment is being transported by the Columbia River and dumped out into the ocean through the Atoria Canyon system and the Atoria fan which is like a submarine fan almost like an aluvial fan that we saw in our last module except for these are underwater here. Right along the deformation front off central Oregon are huge blocks that extend up to 410 m above the seafloor which is well over 1300 ft. Remember it was about the size of the Empire State Building. And we also see that prominent cookie cutter headscarp in the landscape. So this looks remarkable to the landslides that we see on land, right? Except for here we have hundreds of meters of water above our heads. And this particular slide is called the 44 north slide. Here's the eastern half of that seismic profile showing the headscarp in blocks of the 44 north slide as well as a beautiful compressional deformation zone immediately seawward of blocks. See all this probably makes much more sense now towards the end of the semester now that we learned about plate tectonics and deformation. I immediately compared this deformationational feature to what I have observed when shoveling snow or watching a snow plow. Do you now notice the beautiful compressional deformation structures in the form of folds? Remember we talked about folds and that happens when we squeeze rock or sediment. It's compressional deformation. And we can also see thrust faults remember are formed due to compression as well. This zone of deformation is about 275 m thick, which is over 92 feet. So 92 feet thick and it's 10 km long or over 6.2 m long. That's a massive zone of deformation. With this new highresolution data, our reflection data, we can now clearly see that this zone consists of sediment that was originally deposited horizontally. Remember our law of original horizontality that something happened to cause this zone to be deformed and that something that happened was the impact of these landslide blocks. And I actually suggest that this deformation occurred nearly instantaneously. So it wasn't a slow event. It wasn't slowly deformed like a plate tectonics would slowly deform rock. Instead, this was deformed nearly instantaneously. And how do I know that? Well, the sediment on top of this zone is relatively undeformed. So from there I begin to have more questions like why does this deformation zone seem to stop abruptly about 10 km away and how do these blocks retain their massive size and shape after traveling such great distances. Some of these blocks traveled up to 12 miles. I began to wonder if the strain field that we see in the deformation zone gives us information about the forces or maybe even the velocity associated with the slide. And I actually created a mechanical model that reached a terminal velocity of about 60 m/s. That's over 134 mph. And it implies that the buoyancy forces were sufficient enough to uplift the landslide block causing it to lose contact with the surface and hydroplane. So how unique is the 44 north slide? Well, this 44 north side is not unique to this margin. We see at least four other similar events indicated along the southern Oregon margin. Here are two great examples of that in different seismic profiles. So this is different seismic data with a gray scale instead of my red scale that I used earlier. But here below the surface, this is our seafloor. Below our seafloor, we see another kind of chaotic deformed zone with some folds and faults. And we see another one below that. So this indicates that we may have had that 44 north like experiences happening many times in the past. So this is not an isolated event. It has occurred many times in the past and it's likely to occur again in the future. So I then decided to take a look at all of the data we had offshore Oregon and identify submarine landslides in the rock record. And when I did this, I found 133 MTDs, which are uh which stands for mass transport deposit, mass wasting events underwater. So I found 133 mass wasting events underwater identified underneath the seafloor. And here are is a map of showing some of those ones that I found. The ones I found are shown in red. The ones in green are some more recent ones that are found on the sea floor. So I then went ahead and started categorizing these mass wasting events as blocky or disintegrative. Disintegrative meaning that the the blocks broke apart during failure and they were more like a sediment slurry almost like a flow and the blocks relatively retained their shape and slide. So, here's an example of what I did. Here's a seismic profile. This is our seafloor. Here are slopes. We're in a basin. So, we're we're right like in a valley almost underwater. And you can see here there's a blocky slide found right here. And then there's even two more slides beneath that in these semi-transparent zones that are disintegrative in nature. And again, I found 133 of these. And I categorize every single one as blocky, disintegrative, or we have a rotational slump that we talked about. We also see rotational slumps underwater. So I wanted to compare the entire organ margin, split it up from the north and the south, and see if there are any differences between the two. And in the north, we found that these mass wasting events are more common, but they're mostly disintegrative in nature, and their thicknesses range from about 7 and 12 to 70 m, so on average about 65 ft thick. In the south, they are less common, but they tend to be blockier than the ones that we saw in the north. And these thicknesses, more importantly, range from 13 1/2 to over 410 m. So on average, they were nearly 200 ft thick. So the higher frequency of slope failure in the north may not actually indicate an increased risk of tsunami as these failures tend to be small and less cohesive. The frequent occurrence of submarine landslides might actually lessen the chances of a larger blockier slide with a more tsunami generating potential than what is observed in the southern Oregon margin. So in summary, although the slope failure events are less common in the north, I suggest that the southern Oregon margin is actually the one at higher risk of a landslide induced tsunami. So offshore Oregon isn't the only place for concern. There is evidence of massive debris avalanches off the Hawaiian Islands where the slopes of the shield volcanoes can become very unstable and collapse completely into the sea. Take a look at what seafloor mapping has revealed off of Oahu of the Hawaiian island chains right here. These blocks preserved on the seafloor are much larger than my 44 north slide. They're the size of islands. Imagine the tsunami that would have taken place with a slide of this magnitude. All right. Even if mass movements don't cause the loss of life, they do cause tremendous damage and cost billions of dollars worldwide. So, it is so important that we study them. In the next video, we'll take a look at some of the controls on slope stability.