| 00:02 | Started. Uh This would include She wants to uh ask a question |
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| 00:09 | chat. Do either of you have questions on what we've covered? Uh |
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| 00:14 | all morning, but especially the last . Yeah. Not yet. |
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| 00:24 | Alright, fair enough. Let's shift now and begin to look at various |
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| 00:30 | systems and let's start with alluvial And um as usual, there's a |
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| 00:37 | of readings that are useful. Um again, as I mentioned earlier, |
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| 00:44 | the main thing you need to to is what I show in the power |
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| 00:50 | and these and others are available in reading section of the course. That |
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| 01:00 | when we, when we look what are the variables that control alluvial |
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| 01:06 | mythology? Uh Brain injury in relief a biggie. Uh That's tectonics, |
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| 01:13 | source material and sediment supply. That's and climate discharge rate. That's |
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| 01:23 | Area of confinement in accommodation space. basically the whole in which the alluvial |
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| 01:30 | is filling. Uh That's tectonics base . In some cases it's use static |
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| 01:37 | other cases, it is uh locally by uh tectonics, water level, |
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| 01:44 | . Uh That's mainly tectonics and Now, the process is by which |
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| 01:53 | fans developed that morphology are mainly debris , sheet flows and stream flows. |
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| 02:00 | this is where we begin to introduce other ways of sediment transport and |
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| 02:07 | Okay, so here's an alluvial fan the field. We've got a |
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| 02:13 | small drainage area and then a uh confined area. That is an alluvial |
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| 02:23 | being deposited at significant breaking slope. really as much as anything That's where |
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| 02:31 | fans for at this major breaking Now we can study them in the |
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| 02:36 | . We can reproduce them in sand . Uh, this actually is a |
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| 02:41 | that got his PhD here. and uh, engineering is working out |
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| 02:47 | . We can even visualize it in quarries and uh, so there's a |
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| 02:53 | of ways of studying these fans. , the other thing that, that |
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| 02:58 | want to focus on here is that do not occur in isolation. They |
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| 03:04 | in certain tectonic and geologic settings and have co eval, uh, de |
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| 03:12 | systems, uh, that they are related to this particular case in Death |
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| 03:18 | , It's a fault bounded half in which fans great into apply a |
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| 03:24 | . If we had taken this picture years ago, it would be a |
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| 03:30 | of fan deltas depositing into a 100 deep of 101 100 m deep lake |
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| 03:38 | system. So we're gonna be talking fans, lakes, aeolian systems all |
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| 03:47 | gonna be tied together because all of systems often occur and are genetically |
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| 03:55 | Now, fans often do not occur isolated pods. They occur along linear |
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| 04:04 | , usually fault bound. And where have this lateral coalition of fans. |
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| 04:11 | here in the Death Valley. it's called Bahana is basically a broad |
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| 04:18 | area of adjacent Kalev alluvial fans. , one of the things I point |
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| 04:25 | is that here in Death Valley on left, we have the raw |
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| 04:29 | uh, fans on the right. don't see it here yet, but |
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| 04:34 | are much smaller fans. In the slope, uh, whether the |
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| 04:42 | relief of the fans on the northern , it's actually north, its eastern |
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| 04:49 | of Death Valley is different. So gonna see a big difference in fans |
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| 04:55 | the east and went well on the , two opposing sides of uh, |
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| 05:04 | and half Robin's, not only in systems, but uh, throughout the |
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| 05:09 | record. Uh, here's that that broad Baha to on the western |
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| 05:16 | and here we have a much coarser grained uh, series of |
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| 05:23 | uh, sitting right at a fault . You can actually see the false |
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| 05:30 | . Um, here's a little scar . Here's a little scarf right here |
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| 05:40 | this broader scarfs all along here. , at the head or apex of |
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| 05:48 | . Modern fans in particular, we to have, uh, entrenched uh |
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| 05:54 | , radio streams like this is a example of an entrenched fan head. |
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| 06:01 | , and this is what it might like from a distance. Okay, |
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| 06:05 | , um, here's one of those carbs. There's another little one here |
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| 06:13 | uh, the fan goes from an upper fan to a lower fan. |
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| 06:20 | actually has deposition that if we draw cross section through here, might look |
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| 06:27 | like this where we have the upper . Entrenched fan with an abandoned upper |
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| 06:35 | surface that's right here and then we a deposition low down below and right |
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| 06:39 | here is what's called the intersection point we go from erosion to deposition. |
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| 06:45 | is literally a source to sink albeit a subsystem. Okay. And |
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| 06:52 | would be an example of that uh we have the abandoned fan surface up |
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| 07:08 | and actually there's another somewhat younger one here. We have this intersection point |
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| 07:14 | this broader deposition road. Yeah, what we have the same thing down |
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| 07:22 | as well? Uh so that's basically of looks like this. This is |
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| 07:30 | stage in the development of many alluvial where the fan has shifted its entrenched |
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| 07:39 | has formed this outer load. now these fan head cycles where we |
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| 07:48 | , uh, and I should have a little more specific um, when |
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| 07:54 | have fans building up and then being , took off an entrenchment cycle. |
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| 08:03 | . And it could be caused by changes, changes in the slope stress |
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| 08:13 | of just associated fans at all. it could be a low cyclic |
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| 08:18 | tectonic or climatically induced events. So there's an uplift uh, in the |
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| 08:26 | movement and therefore entrenchment until such time the fan is built again, both |
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| 08:34 | . Um but most often it's associated cycle changes. And this is an |
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| 08:42 | again from doug Hambleton um about how things occur. This is by the |
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| 08:48 | from a big sandbox experience. Uh basically the fan is depositing sediment uh |
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| 08:58 | entrenched here. Um So let's deposit . Okay then it entrenches. |
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| 09:09 | And the entrenchment is followed by her deposition. That deposition begins to infill |
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| 09:20 | entrenched up fan system it in in it until such time as it shifts |
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| 09:35 | , it starts all over. so we've got this pattern of well |
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| 09:44 | cutting channel stabilization, low expansion and low deposition. That flow expansion is |
|
| 09:52 | right here. Okay, so the is expanding, diverging flow erosion |
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| 10:06 | Yeah, so low expansion, low , it begins to below retreats |
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| 10:15 | You finally have aggregation of the whole surface followed by avulsion and down |
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| 10:22 | So this is what it looked like that experiment. We had a whole |
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| 10:29 | um inside channels lobes working their web and shifting back and forth. And |
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| 10:38 | basically looked like what 40 years or years earlier Stan Schum had described about |
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| 10:48 | series of entrenchment lobe upstream deposition of upstream deposition etcetera. Okay, so |
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| 11:04 | is pretty much how fans work. is just a little more detailed study |
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| 11:08 | where we actually can see the little that are associated with the fan |
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| 11:19 | The channel moving out here, giving this kind of a low bait |
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| 11:24 | Okay uh and then here notice there's new channel cutting. This was the |
|
| 11:30 | channel down here. So we're getting lot of expansion. This actually right |
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| 11:35 | would be if you like the the uh, scarf. Okay, so |
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| 11:43 | our channel lobe. Earlier stack lobes upstream. And this again is just |
|
| 11:54 | of a view of it. if you look at this diagram in |
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| 11:58 | middle, um you see a series what looked like meandering streams and then |
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| 12:07 | nose like this. Well, these actually debris flow channels and debris flow |
|
| 12:14 | . So this is the beginning of sedimentary gravity flow that really doesn't behave |
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| 12:26 | anything we've talked about earlier. So before warned that the morphology and sediments |
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| 12:38 | these channels and lobes as seen here are gonna be psychologically different. |
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| 12:51 | now, before we get that here's that entrenchment. No another |
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| 12:59 | So this is a story we see fault bound margins all over the world |
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| 13:06 | tectonic li uh driven uh marked boundary is now one of the things I |
|
| 13:14 | here, see, this is this is light. We got all |
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| 13:18 | of color variations here. Uh This out to be an important thing for |
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| 13:23 | fan studies because what we're looking at the progressive aging of abandoned plants, |
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| 13:30 | surfaces. When a fan is those cobbles at the surplus begin to |
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| 13:39 | what is usually a magnesium oxide was referred to as a desert varnish. |
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| 13:45 | the thickness and darkness of that oxide a function of how long it's been |
|
| 13:51 | to the hair. And so we look at and established look at Death |
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| 13:58 | . Um Alluvial fans and establish a uh based on the relative color color |
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| 14:12 | . Uh We can then begin to out the age of those surfaces and |
|
| 14:19 | see that this fan over here actually an oldest portion. It's around 300,000 |
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| 14:26 | old and the youngest portion down here within the last 24,000. So what |
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| 14:34 | to be a single fan is actually aggregate fan formation and entrenchment over Over |
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| 14:46 | years. Now the processes by which fan grew are mainly sedimentary gravity flows |
|
| 15:00 | fluid gravity flows. Fluid gravity flows means water is flowing downhill because of |
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| 15:08 | . A sedimentary gravity flow is because sediment gravity, I'm sorry, a |
|
| 15:15 | water mixture is flowing down because of density of that mixture. That sediment |
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| 15:24 | mixture. It's also gravity propelled but the the effect of the settlement causing |
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| 15:32 | density to flow downhill. Okay, so there are some other processes, |
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| 15:40 | are all secondary processes and I'm not run through the list but just recognize |
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| 15:46 | once that fan is abandoned or rather portion of the fan is abandoned, |
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| 15:51 | things are gonna happen. There's gonna wind winnowing, There'll be plants |
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| 15:56 | there will be soils development, groundwater and set Okay, some of which |
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| 16:02 | will have a be recorded in the a record and some of which probably |
|
| 16:07 | . Okay so let's look at that sediment and fluid gravity flows. So |
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| 16:17 | start first of all with the mass and then we'll look at sheep flow |
|
| 16:22 | stream flow. Okay. Now going to that thing, we looked at |
|
| 16:29 | that stress strain diagram. Um it's on his side which is a little |
|
| 16:36 | but um it shows that with newtonian and even non newtonian fluids that is |
|
| 16:46 | those whose disgusting could change the Um If they have no newtonian fluids |
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| 16:52 | no shear strength. Okay tilted just little. It flows on the other |
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| 16:58 | being in plastic and some other types material including the Celtic lava flow um |
|
| 17:05 | a sheer strength and they only begin move when the applied shear stress is |
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| 17:12 | than its shield strength. Yeah. it can either be a straight line |
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| 17:16 | curve line just like newtonian fluids. what can we say about him? |
|
| 17:21 | the one they have a high they have a sheer strength. They |
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| 17:26 | a sheer strength in part because they a high viscosity because they have a |
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| 17:32 | viscosity. They typically exhibit laminar Remember what I said about the the |
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| 17:40 | number the way you can keep it low and therefore have laminar flow is |
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| 17:46 | increase the denominator. That was the . Okay. Uh It has a |
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| 17:52 | viscosity because it has a high concentration sand and clay and because it's laminar |
|
| 18:01 | tends to be non erosion, it to be a slug of sediment sliding |
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| 18:08 | the other set. Now in the stuff we talked about and going |
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| 18:19 | debris flows is gradation and its gradation . And the function of the sediment |
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| 18:28 | . So we can think of hyper close the three flows. Oh this |
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| 18:42 | um lady is completely great. So gonna kind of treat the end members |
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| 18:53 | the light is gonna be the stuff talked about in river for the most |
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| 18:57 | . Uh And on the left, stuff on alluvial fans recognizing the disk |
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| 19:03 | . So what does that deposit look ? Well in the low especially uh |
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| 19:10 | going to be oily sorted, matrix . And what that means is that |
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| 19:18 | instead of grain to grain contact, we have in uh all the stuff |
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| 19:24 | talked about earlier with respect to uh transport, large grains are separated by |
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| 19:31 | finer grained matrix. Okay. Uh real orientation of the class, no |
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| 19:39 | structures. This is pretty amorphous. , and I might add usually non |
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| 19:46 | base. Now on the right is description. Uh It really is more |
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| 19:56 | . This is based on field for again, uh a fairly short |
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| 20:04 | Uh may have a little erosion often erosion. Notice the um Now listed |
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| 20:14 | here, the matrix support in some a little bit of class supported. |
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| 20:22 | maybe on occasion, a little bit group Betty it made great up into |
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| 20:30 | role cards followed by another degrees loan of these packages, oops, it's |
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| 20:51 | be a bounding service And internally we have lower order founding services trying to |
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| 21:05 | this to the flu real founding Uh the largest ones are probably gonna |
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| 21:13 | uh separating events. But the problem , and if debris flow it doesn't |
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| 21:22 | as a single event. Sometimes they're and so each of those surgeons is |
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| 21:28 | to give us a little bit of pack. So some places here we |
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| 21:35 | have delineated the whole event but that is subdivided the searches, other things |
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| 21:43 | so it's much harder to apply the of bounding surfaces to debris flow deposits |
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| 21:49 | it is safe for. Uh the deposits the same now because alluvial fans |
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| 21:58 | often very coarse grained, gravel Uh we use this type of shorthand |
|
| 22:05 | again notice that uh we got three . Matrix support. Last supported. |
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| 22:16 | across strategy cleaner. We've seen already supported. Okay. Uh basically the |
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| 22:26 | grains are attached to each other not by each other. Um There may |
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| 22:32 | may be completely massive. You might a crude betting maybe some inverse rating |
|
| 22:39 | then in electric support him, it be just massive or it could be |
|
| 22:43 | . So these are kind of our hands. Uh and I'm not gonna |
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| 22:50 | you to use it, but I'm ask you to remember that. It |
|
| 22:54 | be used. So I have something assignment, I might say, and |
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| 23:01 | your best turn for. But on example would pass for that. But |
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| 23:06 | is a matrix supported ungrateful. Did flow? And obviously they're pretty |
|
| 23:12 | can be pretty thick and the class pretty large. Okay, so it |
|
| 23:17 | be a G. M. Uh in that previous category. Now |
|
| 23:23 | said you could go to a sand or quarry and actually study alluvial |
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| 23:29 | Uh That's in part because even at scale, it's a show scale. |
|
| 23:36 | see a series of sandy debris And there's a channel here with the |
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| 23:47 | lobe. Here, here are those lobes and the channels themselves a little |
|
| 23:59 | to tell here, but they actually levies. A debris flow channel is |
|
| 24:06 | defined by two parallel levies. And so here the channels are up here |
|
| 24:14 | then we have these overlapping lobes. , this is in a little sand |
|
| 24:22 | , this is at the base of mountain. But we see the same |
|
| 24:27 | . These are just coarser grain bigger flows with those elongate lobes. And |
|
| 24:37 | here little livy to re flow channels this is even a bigger one where |
|
| 24:52 | looking at a lahar which is a debris flee with those parallel ladies. |
|
| 25:02 | these overlapping debris flows and in this example, which is kind of typical |
|
| 25:09 | loads here. Okay, so this is typical of this type of |
|
| 25:22 | Your gravity flow. It's actually typical any said any gravity flow. |
|
| 25:27 | if I I could show you a um and acidic lava flows, the |
|
| 25:34 | Vesuvius, it looks just like this at least has the same components. |
|
| 25:38 | . And one of the characters very front, steep front here, which |
|
| 25:44 | a function of its viscosity. levy channels, state front. |
|
| 25:52 | so morphological e debris flow sit at end of a triangular classification skin. |
|
| 26:04 | this is from Galloway book, bill uh kind of made his name on |
|
| 26:09 | classifications. Everything he does does or it kind of puts into a triangular |
|
| 26:16 | . Uh As we'll see there is question about what's gonna go on over |
|
| 26:27 | . I'm actually kind of making fun me and I went to school |
|
| 26:31 | so I know him better than Um but debris flows clearly represent one |
|
| 26:38 | process and the brief and and alluvial that are predominantly debris flows represent one |
|
| 26:48 | member of alluvial fans. Okay. so they tend to uh have in |
|
| 26:55 | channels that are subsequently filled. We that in the experiment in a lower |
|
| 27:03 | characterized by the lobes. Ok, here is a a debris flow fan |
|
| 27:12 | the lower zone more distal zone being . In the upper zone, mainly |
|
| 27:21 | are the mainly channel dominated. so, well what each of these |
|
| 27:31 | look at, notice we've got a of overlapping lobes and over here these |
|
| 27:38 | older lobes. When the channel was in this direction, those lobes |
|
| 27:44 | it shifted, these lobes will backfill it'll shift again. So here's one |
|
| 27:51 | flow fan, uh the dolomite fan you can actually look at the morphology |
|
| 27:59 | individual debris flows and you can actually them and they look just like these |
|
| 28:04 | flows in this case in Alberta Okay, And this is dating |
|
| 28:11 | Uh the blue was 1980 for Okay, so you see how this |
|
| 28:18 | shifted an old one and the new shifted on either side. Another one |
|
| 28:24 | come down here etc. So what look like here are the levees, |
|
| 28:33 | basically just parallel gravel lobes. and here they are in process down |
|
| 28:44 | . Now, if we took a down flow, we have the levee |
|
| 28:50 | up here at the levee channel with channel base and then the lobe itself |
|
| 28:58 | matt you coming down like this. there is in fact a little bit |
|
| 29:04 | oriented gravel's not always but there can oriented gravels there still crude, they're |
|
| 29:11 | really well bedded but they tend to somewhat aligned and that actually isn't too |
|
| 29:18 | in laminar flow. Sometimes you get flow alignment, but the upstream portion |
|
| 29:29 | cross section is very different than that section in cross section. So |
|
| 29:37 | it might look if you were trying model it with an upstream levy dominated |
|
| 29:44 | or up fan that are said in down fan. Loeb dominated grading into |
|
| 29:52 | is beyond the fan, it could a lake, it could be a |
|
| 29:56 | , it could be a aeolian it could be a plan cross section |
|
| 30:02 | , mainly those in those uh, Ized um levee systems and then down |
|
| 30:16 | , mainly those overlapping lobes. so that would be your debris flow |
|
| 30:23 | . Okay, this is somebody else's of the same thing. The main |
|
| 30:29 | though saying yes, levies and Now this is Owens valley, big |
|
| 30:41 | here, fault over here and we're look at some fans coming down this |
|
| 30:50 | just at the base of the sierra . Now at first it kind of |
|
| 30:58 | like these are just streams, But we, and this is one fan |
|
| 31:07 | out, here's another fan, it like a distributor, very stream |
|
| 31:15 | But if we look more closely we that these are actually levied channels and |
|
| 31:22 | double levees here, these are all long lived debris flows. They're coming |
|
| 31:33 | as narrow chan and they just stay way and then form a lobe a |
|
| 31:37 | . Okay, now we just saw earlier with the Dolomite fan, but |
|
| 31:44 | difference is one scale, the dolomite is not a very large, in |
|
| 31:49 | it's a tiny fan. Okay, the portion that's levy dominated. So |
|
| 31:56 | of these fans that are forming at base of major false cars. |
|
| 32:02 | and therefore our analog for many basin systems, uh, are really large |
|
| 32:15 | with a lot of debris flow levies the globes being farther out. |
|
| 32:24 | The other thing to know is that we saw with other fans when we |
|
| 32:31 | at their age, there's a lot different ages, which implies there's gonna |
|
| 32:34 | a lot of, it's section incision Phil cut and fill. Cut, |
|
| 32:39 | . Um, here you're looking at or six stages of fan development just |
|
| 32:46 | the last 80,000 years. Okay, that's one end member, a small |
|
| 32:54 | a large degree flow fan. Let's down here cheap now in sheep, |
|
| 33:04 | the dip, right? Which is term we use for a deposit formed |
|
| 33:10 | debris flow. Dead rights. were pretty uh nondescript. They do |
|
| 33:20 | lobes do have levees, but not else. Heat floods are basically floods |
|
| 33:31 | they they're not channels, they're non eyes, sheet flow water and as |
|
| 33:39 | result, they're typically class supported. other words, there's more water here |
|
| 33:46 | there are on debris flow fans. we have lower viscosity, it's more |
|
| 33:54 | light, but it's still gravel rich so the gravel tend to be |
|
| 34:01 | like we would see and um blunder in our braided stream and they tend |
|
| 34:08 | be graded going from coarse to fine a single event. Little better |
|
| 34:15 | So let's say moderately stories so much sorted than debris flows. And so |
|
| 34:23 | is what it might look like. and one of the is that as |
|
| 34:32 | slow way to get together, try find sands and we see some more |
|
| 34:42 | the face. So whereas the debt were largely non erosion. As those |
|
| 34:50 | are coming over the surface, cheap is turbulent flow, it's gonna be |
|
| 34:57 | at the bottom, so it's gonna more like the left with this model |
|
| 35:02 | . Okay, uh again, we're to talk about in size channel. |
|
| 35:14 | hears the inflection point, here's the , it's gonna shift. Okay, |
|
| 35:22 | , here's the debris flow fan and that cheap little thing, It's still |
|
| 35:29 | the potential for being entrenched, but the lobe is much more uh deposit |
|
| 35:42 | sheet flow and the little streams that in here, they're often post flood |
|
| 35:50 | there's a, you get a slug of sand coming down with the sheep |
|
| 35:56 | then later you begin to get it slightly by surface erosion. But the |
|
| 36:05 | process in entrenchment upstream, avulsion upstream upstream. So, our, our |
|
| 36:17 | for that, we're gonna go to Death Valley and we're gonna look over |
|
| 36:25 | and we're gonna look at one of fans that we actually saw pictures |
|
| 36:28 | But before I do that, let focus on the structural setting of Death |
|
| 36:33 | . Because it turns out it's a for basins all over the world. |
|
| 36:42 | a half rob. Okay. Which pretty typical, both of extension allow |
|
| 36:46 | trans intentional basis. Okay. And a master fault and then there is |
|
| 36:57 | kind of a marginal zone that may may not be faulted, but the |
|
| 37:03 | isn't too much. So this is much more gentle slopes, steeper |
|
| 37:09 | This tends to have a much larger area. And over here. |
|
| 37:16 | the Black mountains, here's the drainage , The Panama Mountains, here's the |
|
| 37:20 | divide. So there's a much larger feeding these fans. Okay. We |
|
| 37:30 | a couple of pictures of little debris fans over here earlier. But now |
|
| 37:35 | want to talk about larger fans on opposite side of that particular Robin |
|
| 37:44 | probably. And we can break them into um four little fishies, little |
|
| 37:53 | a through d uh d actually, let's let's go start up here, |
|
| 38:07 | sandy couplets. You've got plainer bedded inter bedded with planer bedded sands and |
|
| 38:18 | ground. Okay. All poorly sorted supported. It's most of the |
|
| 38:27 | So it's that that is the sheet deposit. Yeah. And it looks |
|
| 38:34 | this. So most of that fans consist of cheap flow deposits and they |
|
| 38:42 | of look like this. Um Here's base, Here's the base of the |
|
| 38:48 | one Face. The next one. you see here there's a little sandy |
|
| 38:55 | . Sandy top. Okay, that's gravel sandy coupler. Okay. And |
|
| 39:04 | can see that it pretty much is bulk of that fan as exposed. |
|
| 39:14 | second is not a major component except the upstream, It can be up |
|
| 39:23 | 25% in the proximity and it and not found at all downstream. And |
|
| 39:31 | their upstream dipping cross strap in lenticular . That's upper floor, pretty cheap |
|
| 39:40 | . That's like the anti dunes and shooting pools like this is a picture |
|
| 39:45 | one um is within that sandy portion the couple it, but now you've |
|
| 40:01 | upper flow regime conditions in the sheet . And so those would actually be |
|
| 40:14 | here and I call it in any . I'm not sure if that's i |
|
| 40:24 | hindsight. Uh That's probably more like shooting pool. It's really too big |
|
| 40:31 | too steep, dude. So And B. The sandy gravel, |
|
| 40:45 | couplets and those little back wedges or forming this fan. Yeah. Uh |
|
| 40:54 | but rapid or water coming in from rain or snow sets of half a |
|
| 41:02 | to 2.5 m high preservation potential. other stuff basically, it's mainly stuff |
|
| 41:18 | the end of the flood, post . So it's kind of reworking what |
|
| 41:25 | else is. So it's not gonna very common. Yeah, the difference |
|
| 41:34 | uh they are the uh B are wet shapes from upstream course. |
|
| 41:56 | it's gonna be within the sandy portion the Yeah, I mean, water |
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| 42:05 | smoothie, there's a sheep just get perform regime and it upstream And they |
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| 42:24 | be up to 25% of the upstream . You don't get them downstream on |
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| 42:31 | more digital portion fan because the water lost serious things. Okay, so |
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| 42:41 | , these are some of the typical uh that we get on the horse |
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| 42:47 | fans here, that the brief close , is that sheep and I use |
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| 42:56 | flow and sheep flow kind of in . Now, when you get into |
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| 43:02 | strata, graphic records begin to measure sentence. Uh you begin to see |
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| 43:09 | cyclist city and you begin to see of the variation that you get as |
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| 43:17 | fans are growing. Mhm. I'm not gonna get into this particular |
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| 43:23 | study except to say that each of is basically irrational base finding up. |
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| 43:32 | what this looks like and notice I'm make an interpretation here. Uh This |
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| 43:39 | be upstream different here, they don't indicate uh this is pretty much uh |
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| 43:49 | there's most of this looks like it's supported rating upward. Normally graded inter |
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| 43:56 | sand couplets. So we're looking at uh a sheep flocks, sand or |
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| 44:04 | flow, sheep flow. Damn, you. Uh the are some of |
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| 44:13 | insides channel closets. Uh We don't them a lot because they're filled with |
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| 44:22 | flood deposits. But they're they're gonna little bit better. Mhm stratified. |
|
| 44:32 | may be cross stratified. Um They have lenses where they they're filled. |
|
| 44:39 | gonna geometrically, there aren't gonna be extensive, so biometrically they're not that |
|
| 44:46 | . So when we look at the fan changes in the relative abundance of |
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| 44:56 | , the side channel are real abundant . You wouldn't expect it to. |
|
| 45:08 | set wedges are restricted to the higher portion of the family. The couplets |
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| 45:21 | and B. Pretty much fill the form the bulk of the often and |
|
| 45:27 | we see up in here occurs pretty all of the this is the surface |
|
| 45:35 | um little gully films. This So biometric and this is not a |
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| 45:43 | section, it's a relative sense of exposure. So these will probably occur |
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| 45:51 | throughout the thing, what this does simply who is about to fill their |
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| 45:59 | abundance. So keep in mind, is not a cross section, but |
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| 46:03 | just a relative abundance and the change relative abundance downstream. So this is |
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| 46:10 | like what it looks like the sheep couplets. The back sets science channels |
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| 46:18 | course here we see integrating with looks you're incorporating into base and floor deposits |
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| 46:27 | they want. Mhm. And so can also take cross sections, the |
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| 46:36 | fan or proximal, the lower fan disallow and you can kind of see |
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| 46:41 | that might vary as well. Galloway shows a an interpretation that he |
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| 46:56 | got from that suggests there's an evolution change downstream with Spanx. Uh, |
|
| 47:10 | that's true, but this this call such a need some interpretation. We |
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| 47:17 | see a decrease in class size Now that is due to selective |
|
| 47:25 | Remember when we talked about downstream we could have abrasion and that that |
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| 47:31 | cause downstream decreasing size and big That's not happening basically up And five |
|
| 47:42 | at 22. Now, selected pastors the course dropping off first can only |
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| 47:51 | over long periods of time if you creating accommodation space, uh, thickness |
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| 48:01 | , channel depths, annual decrease, ratification increase story, so they kind |
|
| 48:08 | view them going from the three flows shape, but that's not really what |
|
| 48:17 | show process. They show this chaos into an underlying degrees. Breaking up |
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| 48:29 | a larger programming cheaper at that. so this actually may be a good |
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| 48:42 | of how a fan might change with from an earlier, well later she |
|
| 48:52 | . Now one of the ways to that, remember for two brief low |
|
| 48:56 | , the a preponderance of set and much water to get that high |
|
| 49:07 | etcetera. So, think of the area, the drainage basin is feeding |
|
| 49:15 | fact, it's smaller. Okay, as long as the politics continue, |
|
| 49:20 | can stay small. But what happens the politics slows down, You can |
|
| 49:25 | to enlarge the drainage area. what happens when you enlarge the drainage |
|
| 49:31 | , you get more water coming out that, same speaking, so you're |
|
| 49:40 | to go into or keep flood high deposition. So we might well see |
|
| 49:52 | kind of obsession if there is a in the sources which in the case |
|
| 49:59 | alluvial fans is often tectonic lee driven could be driven my client dry |
|
| 50:04 | But now we can actually see an of that in an alluvial fan in |
|
| 50:12 | in Sweden. We think of alluvial as a desert feature and we think |
|
| 50:20 | them as forming at a Foxconn, that's just because we've studied more vaulted |
|
| 50:29 | alluvial fans. They occur in all of places. What you need is |
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| 50:35 | steep scarf, an abrupt change of . So what we have here is |
|
| 50:45 | a false car but a glacial This is the edge of a U |
|
| 50:50 | ballot. This is a hanging valley is now filling that valley fill was |
|
| 50:59 | little girl fan. Okay, that's first thing. Now it turns out |
|
| 51:06 | can look at that alluvial fan with and you can recognize different radar fishies |
|
| 51:16 | little thinks she's an outgrowth and and what you see is a transition from |
|
| 51:28 | lower debris flow, fans, the boat, the flower shed blood, |
|
| 51:39 | still get to re close, we get cheaper, but the relative abundance |
|
| 51:45 | shifting from debris flow dominated constraints. it's the same fan in your |
|
| 51:54 | but it's just evolved over time. and the reason basically is because of |
|
| 52:01 | change of climate consortium that hanging valley from glacial conditions to warm, wet |
|
| 52:12 | , so, or wet or Okay, yeah. The original work |
|
| 52:24 | really the seminal work of Larry and looked at and um talked about stream |
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| 52:35 | or rather sheet flood uh and the flow of fans and then they talked |
|
| 52:47 | rivers that are called fans because in interpretation, if you look at the |
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| 52:56 | of the these little fans that we've about Nick 10, maybe 10 km |
|
| 53:03 | the Apex they're very state. And we have other fans or things that |
|
| 53:09 | call fans that are very low So here are rivers and here are |
|
| 53:20 | are called fans. So what they're is they're not really fans now Galloway |
|
| 53:30 | them alluvial fans or dream flow but we're gonna talk about what is |
|
| 53:41 | with these larger and larger fan shaped . Now, one of the things |
|
| 53:48 | when you have really steep gradients, tend to have a hypocritical form, |
|
| 53:57 | know the manage manage number is just about, thank you. This is |
|
| 54:05 | we get, oh, most of , oh yeah, by the time |
|
| 54:16 | get down to these roads, you're some credible for me. So de |
|
| 54:27 | surprised lower for regime dominates rivers, a surprise for the acquis portion of |
|
| 54:40 | , it's dominated by, or at uh, as a strong component |
|
| 54:48 | of course, a lot of it actually, uh, not it's |
|
| 54:58 | So they say, you know, this gap, there's this natural gap |
|
| 55:06 | , they fall slow between what they a real alluvial fans. They think |
|
| 55:13 | rivers fans and, and so what suggest is the fault in thinking of |
|
| 55:24 | . As anyone of things, hear your grief flow the sheep blood. |
|
| 55:33 | see this creation, uh, as get one more water less and less |
|
| 55:42 | flows, a little larger and larger here we got good example. But |
|
| 55:51 | when we look for example, they look very different now when the |
|
| 56:01 | a really big and they can because any number of things mega fans |
|
| 56:13 | common. This tributary feudal system is the most common. We used. |
|
| 56:27 | was suggested that these are the these are long, but it's not |
|
| 56:37 | well, they're river deposits, they're confined channels, but they have a |
|
| 56:43 | pattern. So here are those fans just briefly and here are these alluvial |
|
| 56:55 | . Really bad. It's distributed. , I've chosen to deal with these |
|
| 57:06 | a part, but having said um, what I would point out |
|
| 57:13 | that what all of these fans shaped have, is a transition from confined |
|
| 57:23 | to unconfined rivers and there's an apex here. That's below which the rivers |
|
| 57:31 | split up or migrate and they can very large. What we're really seeing |
|
| 57:39 | a transition not of so much fan , but rather the transition with larger |
|
| 57:47 | larger rivers coming from our larger and drainage areas coming from a confined to |
|
| 57:55 | unconfined, changing slower. So that be well, thank you. I |
|
| 58:05 | because okay. Now one thing I say is that with satellite images, |
|
| 58:17 | have many more examples of back So here's one of the chinese fans |
|
| 58:28 | uh, elsewhere we can calculate the in the distance on google earth. |
|
| 58:38 | another band popular fan. Really, a very nice study for large fan |
|
| 58:45 | clearly meets all the definitions of a surface. Uh, and I'm not |
|
| 58:53 | to get in and notice the little and this bigger fan, we see |
|
| 58:58 | a lot and just simply needs from the tributaries and bigger, larger, |
|
| 59:07 | rivers, bigger fans, smaller training , smaller things. So it really |
|
| 59:15 | that opposite. And so when we at the then compared to the, |
|
| 59:20 | the land handles praise. They got chief flood deposits, yep, unconfined |
|
| 59:31 | and greater stream here. The official and some ponds in the open, |
|
| 59:40 | is unique to specific Uh, fan , 27 km 730 km is it |
|
| 59:53 | ? Well, it's a great extreme . If you look at the down |
|
| 59:57 | areas, you see all sorts of in the brain and strain. That's |
|
| 60:05 | I'm going to talk about these in of rivers, we can see the |
|
| 60:17 | uh, flood can, can curve large areas. This is basically still |
|
| 60:23 | fan at least in terms of what thinking about. But it really has |
|
| 60:31 | into a, I'm fine. What still have cheap, but we have |
|
| 60:44 | lot of okay, confined flow, dreams as well. So I would |
|
| 60:51 | maybe this is still okay to put within that triangular system. It really |
|
| 60:58 | look like an enlarged fan with some extreme components. Um, and so |
|
| 61:07 | happy to call this a fan. now look what we've done. Here's |
|
| 61:15 | proper man saying like this much smaller these larger and larger things. So |
|
| 61:27 | it really a natural gap or as start looking more and more base families |
|
| 61:39 | satellite received more and more that transition terms of slope. Mm These are |
|
| 61:50 | some of the, um, I a class project, I had people |
|
| 61:54 | look for fans and measure them. begin to, yeah, once we |
|
| 62:09 | getting into hey distributed system that's so we could no longer have sheep flow |
|
| 62:20 | debris flows deposits at that point. choosing to treat his risk and I'm |
|
| 62:29 | talk about it and talk about beers said that, what it really |
|
| 62:34 | it's a special case of where the , that rapid shift of river location |
|
| 62:42 | hinge at an apex. So the keeps sweeping back is um, so |
|
| 62:51 | what makes it different. That's what call it, a distributed flu hill |
|
| 62:57 | . And it turns out a lot basin filled is that much larger scale |
|
| 63:05 | be assist it's hands that analysis a outside. Okay, a couple of |
|
| 63:15 | things about fans, small fans. , sometimes they go into lakes or |
|
| 63:25 | and so they form not fans, fan deltas. The importance of that |
|
| 63:31 | that you have a zone of reworking in the distal portion of the |
|
| 63:39 | uh we get better sorted sense. as we think about reservoirs, |
|
| 63:49 | now we begin to see the medial portion of the fan areas of higher |
|
| 63:57 | . It's, and we can imagine and important, uh Reagan streets and |
|
| 64:12 | deal Finally what's called fine green Now, I'm not gonna use this |
|
| 64:22 | called common delta. Um, I use this to state, you accept |
|
| 64:31 | versus a river is an important Can be a little river could be |
|
| 64:44 | . What this, the idea of delta grading into something that is for |
|
| 64:53 | rich um is an important and, a good example of that Is to |
|
| 65:00 | to the next one. You're looking California. It's a narrow peninsula, |
|
| 65:07 | , not the training base. These are very large. So these are |
|
| 65:18 | little alluvial fans raiding directly into the of County Go on the other |
|
| 65:25 | We've got a larger break extreme that Elka formed by greatest and here's the |
|
| 65:34 | basin is always for the question. that's a very different fan going into |
|
| 65:46 | same. Thanks. Here's the greatest here. Here's the and as a |
|
| 66:04 | here too. Types of deltas that feeding that structurally controlled marine trough. |
|
| 66:17 | is a theme we will see even clearly, at least more frequent. |
|
| 66:28 | , let me talk about lake deposits we look at in the custom in |
|
| 66:36 | filling fault bound like Austrian systems. keep this example in mind. |
|
| 66:46 | now, let's go back just a again to talk about what's controlling the |
|
| 66:53 | geometry. We've already talked about this , climate sediment supply base level and |
|
| 67:01 | relative abundance therefore, of different types processes. We've talked about how we |
|
| 67:09 | get auto cyclic changes by simply shifting entrenchment, backfilling, etcetera. |
|
| 67:20 | , so it might look something like . Okay, but we can also |
|
| 67:25 | at a low cycling changes external to base or external to the the the |
|
| 67:34 | itself. For example, climate We we've got in new Mexico good |
|
| 67:44 | of cyclist city within alluvial fans as go from sub humid back to sub |
|
| 67:55 | . Good. Uh, we can at humid, arid image in the |
|
| 68:05 | city and the types of sedimentary structures we might get in these different |
|
| 68:12 | Again, you don't need to know except that their changes in humidity are |
|
| 68:21 | dramatically changes in, in uh, and temperature are gonna change the way |
|
| 68:30 | which sediment is supplied to the All things Another here we have a |
|
| 68:40 | of false carps. So it's not to see fan entrenchment locally formed by |
|
| 68:49 | of uplift. But here's a one those faults. Here's another one. |
|
| 69:01 | see him here and here actually, a pretty big scarf city here. |
|
| 69:08 | what that does is it leads to formation of what was sometimes called hourglass |
|
| 69:17 | where this was they're going getting bigger bigger and then uplift occurred and it |
|
| 69:28 | sharply entrenched. So this is the section. We get actually have something |
|
| 69:34 | this now because active fault fronts are places for Louisville fans occurred. Their |
|
| 69:49 | aggregation depends on the style, location activity of defaulting. So if the |
|
| 69:57 | basically stays in the same place, gonna get a vertical stacking a |
|
| 70:06 | We also have false back step and gonna change the morphology and repeatedly, |
|
| 70:16 | might get something that looked like So the, the cross sectional geometry |
|
| 70:24 | vary with the false history and the thing to keep in mind was at |
|
| 70:29 | . If we went into the that fault is gonna change with distance |
|
| 70:40 | therefore the false activity. We'll see about that. We talked about |
|
| 70:47 | So in this particular example, we a change in relative sea level being |
|
| 70:56 | actually by change in rates of Now that's relative sea level, not |
|
| 71:04 | static sealer. Because what happens is got a lot of tectonics floating, |
|
| 71:12 | land drops. Well, it's sea rise, this trans register. And |
|
| 71:17 | is that voting subsides? You get refresh if so you think stay a |
|
| 71:26 | of pulses, uh, ban coming the basin and out of the basin |
|
| 71:36 | with thrust cycles. Remember what I about the Oakville sansa where you have |
|
| 71:45 | flood of Calcaterra nights coming in. you can tell more about what's going |
|
| 71:52 | in the tectonic lee, update drifting by looking at the basis then you |
|
| 71:59 | in the area, it's frankly all eroded away. So you want to |
|
| 72:04 | mountain building, study base information. levels can change Particularly in uh, |
|
| 72:17 | basins. This is the elevation change place in m over the last |
|
| 72:25 | you know, really over 2000 Over 2000 years, it rose and |
|
| 72:32 | fell almost 60 m. Okay, almost as much as you static sea |
|
| 72:38 | changed and 50,000 years. One of things about alluvial fans had two |
|
| 72:52 | his base level is changing or at has to remember what I said about |
|
| 72:58 | alluvial lakes in the southwest with Death used to be a really deep lake |
|
| 73:07 | years ago. Now it's a Okay, so we're gonna stop |
|
| 73:14 | Okay? Take a break. Um then we will start on likes. |
|
| 73:22 | Let's take about that's coming around to that give you time to do what |
|
| 73:27 | need to do? Not hearing It's 1:45 now? Uh think about |
|
| 73:34 | minutes. |
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