Stop that Sediment! Create a plan to help the people that work, live, and play by the Toutle River

Transcription

1 Stop that Sediment! Create a plan to help the people that work, live, and play by the Toutle River

2 The 1980 eruption began with an enormous landslide.

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4 As far as we know, this landslide was the largest landslide that was witnessed by people that lived to tell the tale. It removed an entire mountaintop! In just a few moments, Mount St. Helens changed From this: To this: Jim Nieland/USFS

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6 How much rock was in the landslide? 4 BILLION Boxes this Big OR 1 MILLION Olympic-sized swimming pools Getty Images/ Lana Oatey Pixabay.com

7 The landslide ended up in the Toutle River Valley as big chunks of rock called hummocks.

8 This is what the hummocks look like today.

9 The hummocks are made of sediment. Sediment is a word for a piece of rock that has been moved from where it originally was, usually by water.

10 Sand is a type of sediment. Sediment can also be smaller or bigger (like the size of powdered sugar) (like pebbles, cobbles, and boulders).

11 After the landslide, not all of that sediment remained in the hummocks in the upper Toutle River Valley A few hours after the eruption, the sediment mixed with water and created a dangerous lahar (or volcanic mudflow) that ripped up buildings, trees, and bridges. USGS

12 The mudflows in the 1980 eruption were devastating. The mudflows ripped up bridges, trees, buildings, and other things in their path. & The mudflows buried things that were at the bottom of the valley.

13 Sediment went into the Columbia River and settled to the bottom, making the river shallower. Some ships were trapped until the river was dredged. Dredging is what people do to make rivers deeper. They use equipment to dig out or suck up sediment. Both of these are dredging boats U.S. Army Corps of Engineers Photo Archives Website

14 How much sediment was in the 1980 lahar? This is a million Olympic pools

15 How much sediment was in the 1980 lahar? This is a million Olympic pools This is about 10,000 Olympic pools

16 The 1980 mudflows were large and devastating, but there s still a lot of sediment in the hummocks.

17 You don t need a lahar to move sediment. You just need a river.

18 It happens much more slowly, but the Toutle River carries a surprisingly large amount of sediment. Each year, the Toutle River moves about 1/3 of the sediment that was moved by the 1980 lahar.

19 It might not seem like much when compared to the mountain and the sediment in the landslide, but It s enough to fill up about 3000 of these Olympic swimming pools! It s a LOT of sediment!

20 This huge amount of sediment may cause problems for the people that work, live, and play by the river for many years to come. If nothing is done to slow or stop the sediment, it could bury things, like the mudflow did. WE NEED YOUR HELP!

21 YOUR MISSION: Design a plan to minimize the effect of ongoing sedimentation in the Toutle River Valley for the next 50 years. This can include: Building a structure Using natural resources Using services (like digging or dredging) or or Army Corps of Engineers USGS or some combination of the three or an entirely different, creative idea!

22 Building a structure This is the Sediment Retention Structure (SRS). The SRS is a dam (a wall that goes across the whole valley). Army Corps of Engineers It has a place for water to escape, so pressure doesn t build and it doesn t burst open.?what other shapes could slow or stop sediment??how big should it be??what should it be made of??how many?

23 Using Natural Resources Buried logs can make a log jam The logs catch some of the sediment. do you think would happen to the way sediment moves if you planted trees or shrubs?

24 Using services (like digging or dredging) USGS Remember: dredging is digging up sediment to make a river channels deeper Cat.com?How often should I dig??where should I dredge or dig?

25 INSTRUCTIONS You will receive a list of supplies and services that you can use. This list is kind of like a Minecraft inventory. Each supply is priced per block. The supply list will tell you how many coins a block of each supply costs. You are on a budget! You may only spend 200 coins. Minecraft

26 downstream This is a view of the Toutle River valley from the side. This is called a crosssection. You will draw your design on this sheet. MOUNT ST. HELENS this way

27 Your worksheet will have a grid on it. Each square means 1 block on your supply list. Minecraft When you design your structure, count the number of blocks of each supply you use. Keep track of how many coins you spend on supplies and services. You can only spend 200 coins!

28 EXAMPLE supplies: 60 cement blocks 6 trees 25 small plants 2 large logs 3 big pipes 6 small pipes 19 chainlink fence =195 coins services: Dredge every 10 years =5 coins = 200