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Dialogue: 0,0:00:01.22,0:00:04.64,Default,,0000,0000,0000,,Chad Kiel: Hey guys, it's Chad Kiel with \NLearning Geology and Nature Reconnection,
Dialogue: 0,0:00:04.64,0:00:07.21,Default,,0000,0000,0000,,and today we're learning about Alluvial\NFans.
Dialogue: 0,0:00:07.21,0:00:08.90,Default,,0000,0000,0000,,What is an alluvial fan?
Dialogue: 0,0:00:08.90,0:00:12.50,Default,,0000,0000,0000,,And I'm going to tell you about some \Ninteresting data about this alluvial fan,
Dialogue: 0,0:00:12.50,0:00:15.14,Default,,0000,0000,0000,,and the processes that created it,\Nbecause it happens to be in
Dialogue: 0,0:00:15.14,0:00:16.32,Default,,0000,0000,0000,,my backyard.
Dialogue: 0,0:00:16.32,0:00:19.50,Default,,0000,0000,0000,,Let's go check it out.
Dialogue: 0,0:00:19.50,0:00:23.52,Default,,0000,0000,0000,,So before we dive down the rabbit hole\Nof alluvial fans, let's first take a
Dialogue: 0,0:00:23.52,0:00:28.06,Default,,0000,0000,0000,,second to talk about weathering and \Nerosion, because those are two factors
Dialogue: 0,0:00:28.06,0:00:30.90,Default,,0000,0000,0000,,that are gonna come into play again and\Nagain when we're talking about this
Dialogue: 0,0:00:30.90,0:00:32.40,Default,,0000,0000,0000,,alluvial fan.
Dialogue: 0,0:00:32.40,0:00:36.30,Default,,0000,0000,0000,,Right here around 6,500 feet into the\Nmountains, temperatures can vary from
Dialogue: 0,0:00:36.30,0:00:42.47,Default,,0000,0000,0000,,20 degrees each day, causing the rocks to\Nkind of expand and contract, and this
Dialogue: 0,0:00:42.47,0:00:45.99,Default,,0000,0000,0000,,expanding and contracting's gonna\Ncause fracturing.
Dialogue: 0,0:00:45.99,0:00:51.64,Default,,0000,0000,0000,,Now these fractures are susceptible for \Nwater to percolate down into the rock, and
Dialogue: 0,0:00:51.64,0:00:55.74,Default,,0000,0000,0000,,when the water freezes in the rock, we all\Nknow that ice has a larger volume than
Dialogue: 0,0:00:55.74,0:00:58.91,Default,,0000,0000,0000,,water, it again fractures out that rock,\Nand these fractured blocks are deposited
Dialogue: 0,0:00:58.91,0:01:05.04,Default,,0000,0000,0000,,here in this active channel, and then we\Nhave the erosion factor that comes and
Dialogue: 0,0:01:05.04,0:01:07.07,Default,,0000,0000,0000,,transports it down mountain.
Dialogue: 0,0:01:07.07,0:01:11.84,Default,,0000,0000,0000,,So that's the beginning process of this\Nwhole alluvial fan story.
Dialogue: 0,0:01:11.84,0:01:15.41,Default,,0000,0000,0000,,Alluvial fans are triangular-shaped\Ndeposits of water transported material
Dialogue: 0,0:01:15.41,0:01:17.42,Default,,0000,0000,0000,,often referred to as alluvium.
Dialogue: 0,0:01:17.42,0:01:21.23,Default,,0000,0000,0000,,There are examples of an unconsolidated \Nsedimentary deposit, and tend to be
Dialogue: 0,0:01:21.23,0:01:25.77,Default,,0000,0000,0000,,larger and more prominent in arid to \Nsemi-arid regions, like we are today.
Dialogue: 0,0:01:25.77,0:01:29.57,Default,,0000,0000,0000,,These alluvial fans typically from in \Nelevated or even mountainous regions
Dialogue: 0,0:01:29.57,0:01:33.69,Default,,0000,0000,0000,,where there's a rapid change in the slope\Nfrom a high to a low gradient.
Dialogue: 0,0:01:33.69,0:01:36.88,Default,,0000,0000,0000,,The river or the stream carrying the \Nsediment flows at a relatively high
Dialogue: 0,0:01:36.88,0:01:41.03,Default,,0000,0000,0000,,velocity due to the high slope angle, \Nwhich is why coarse material is able
Dialogue: 0,0:01:41.03,0:01:43.18,Default,,0000,0000,0000,,to remain in the flow.
Dialogue: 0,0:01:43.18,0:01:48.24,Default,,0000,0000,0000,,When the slope decreases rapidly into\Na relatively plane area or plateau, the
Dialogue: 0,0:01:48.24,0:01:51.47,Default,,0000,0000,0000,,stream loses the energy it needs to move\Nits sediment.
Dialogue: 0,0:01:51.47,0:01:56.37,Default,,0000,0000,0000,,Deposition subsequently occurs, and the\Nsediment ultimately spreads out, creating
Dialogue: 0,0:01:56.37,0:01:58.88,Default,,0000,0000,0000,,the alluvial fan.
Dialogue: 0,0:01:58.88,0:02:03.33,Default,,0000,0000,0000,,As the streams gradient decreases, it \Ndrops the coarse grain material.
Dialogue: 0,0:02:03.33,0:02:07.10,Default,,0000,0000,0000,,It makes swagger of the channel, and\Nforces it to change direction, and
Dialogue: 0,0:02:07.10,0:02:11.69,Default,,0000,0000,0000,,gradually build up a slightly mounded or\Nshallow conical fan shape.
Dialogue: 0,0:02:11.69,0:02:15.89,Default,,0000,0000,0000,,The sediment that results from the erosion\Nin this elevated mountainous region right
Dialogue: 0,0:02:15.89,0:02:21.35,Default,,0000,0000,0000,,here, ultimately flows into the primary \Nstreams and the regions, where the streams
Dialogue: 0,0:02:21.35,0:02:25.26,Default,,0000,0000,0000,,act as a drainage system, and carry the \Nsediment to the alluvial plane, which is
Dialogue: 0,0:02:25.26,0:02:26.54,Default,,0000,0000,0000,,down below us.
Dialogue: 0,0:02:26.54,0:02:30.65,Default,,0000,0000,0000,,Once the sediment exits the feeder stream,\Nthe sediment is no longer confined to the
Dialogue: 0,0:02:30.65,0:02:31.85,Default,,0000,0000,0000,,channel walls.
Dialogue: 0,0:02:31.85,0:02:36.64,Default,,0000,0000,0000,,With this unconfinement, the sediment\Nbegins to fan out, the alluvial fan
Dialogue: 0,0:02:36.64,0:02:40.76,Default,,0000,0000,0000,,becomes wider with increasing distance\Nfrom the mouth of the canyon.
Dialogue: 0,0:02:40.76,0:02:44.61,Default,,0000,0000,0000,,The biggest natural hazard on alluvial\Nfans are floods, and debris flows.
Dialogue: 0,0:02:44.61,0:02:47.100,Default,,0000,0000,0000,,Floods on alluvial fans are commonly \Nflash floods, they occur with little to
Dialogue: 0,0:02:47.100,0:02:53.26,Default,,0000,0000,0000,,no warning, usually have high velocities \Nin sediment transporting capabilities, and
Dialogue: 0,0:02:53.26,0:02:54.95,Default,,0000,0000,0000,,are relatively short.
Dialogue: 0,0:02:54.95,0:02:58.74,Default,,0000,0000,0000,,Modern flood control infrastructure is \Nessential to stop flooding, property
Dialogue: 0,0:02:58.74,0:03:01.77,Default,,0000,0000,0000,,damage, and the loss of life from\Nhappening.
Dialogue: 0,0:03:01.77,0:03:06.61,Default,,0000,0000,0000,,Successful development can and does \Noccur on alluvial fans, even in rural
Dialogue: 0,0:03:06.61,0:03:11.47,Default,,0000,0000,0000,,areas like ours, mitigation measures are\Nutilized; building pads are elevated,
Dialogue: 0,0:03:11.47,0:03:15.54,Default,,0000,0000,0000,,obvious drainage paths are left \Nunobstructed, and in some cases,
Dialogue: 0,0:03:15.54,0:03:17.29,Default,,0000,0000,0000,,flood walls are built.
Dialogue: 0,0:03:17.29,0:03:21.25,Default,,0000,0000,0000,,Floodplain management principles of\Nalluvial fans are part of everyone's
Dialogue: 0,0:03:21.25,0:03:24.27,Default,,0000,0000,0000,,life that chooses to live in this special\Nplace.
Dialogue: 0,0:03:24.27,0:03:28.24,Default,,0000,0000,0000,,I hope this helps you understand more \Nabout alluvial fans, and the processes
Dialogue: 0,0:03:28.24,0:03:29.44,Default,,0000,0000,0000,,that create them.
Dialogue: 0,0:03:29.44,9:59:59.99,Default,,0000,0000,0000,,Until next time, I'm Chad Kiel.