Erosion

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Objective

SWBAT define erosion as the gravity driven process of erosional particles | SWBAT describe the relationship between sediment particle size and stream velocity

Big Idea

There is a key relationship between stream velocity (how fast its moving) and the size of sediments that can be moved by that stream. Using this idea, students explore what erosion really is - the transport of weathered sediments to a different location

Lesson Introduction

This lesson serves as a natural continuation of yesterday's lesson on weathering. In this lesson, we focus on the overarching concept of erosion as well as highlighting some major erosional agents - water & mass movement (gravity) being the two primary examples. We also break down the Relationship of Transported Particle Size to Velocity chart on the Earth Science Reference Tables [ESRT].

[Note: For embedded comments, checks for understanding (CFUs), and key additional information on transitions and key parts of the lesson not necessarily included in the below narrative, please download the comments in the following document: 7.5 - Erosion (Entire Lesson w/comments). Additionally, if you would like all of the resources together in a PDF document, that can be accessed as a complete resource here: 7.5 - Erosion (Entire Lesson)[PDF]. Finally, students may need their Earth Science Reference Tables [ESRT] for parts of the lesson (a document used widely in the New York State Earth Science Regents course) as well.]

 

Do Now

10 minutes

Students come in silently and complete the (attached) Do Now. In this case, the Do Now is a review of material and some "hot standards" from various units earlier in the year, including Earth's history, Rocks & Minerals, and Meteorology. After time expires (anywhere from 2-4 minutes depending on the type of Do Now and number of questions), we collectively go over the responses (usually involving a series of cold calls and/or volunteers), before I call on a student and ask them to read the objective out loud to start the lesson. 

As a general note, the Do Now serves a few purposes:

  1. It serves as a general review of the previous day's material;
  2. It is a re-activation of student knowledge to get them back into "student mode" and get them thinking about science after transitioning from another content area or alternate class;
  3. as a strategy for reviewing material students have struggled with (for example, using this as a focused review for material that they have struggled with on unit assessments or recent quizzes); and,
  4. It is an efficient and established routine for entering the classroom that is repeated each day with fidelity (I never let students enter the classroom talking. While it may seem potentially severe to have students enter silently each day, this is both a school wide expectation and a key component of my classroom. In many respects, I find that students readily enjoy the focus that starting with a quiet classrooms brings each day).

Notes & Video

20 minutes

The first twenty (20) minutes of the lesson involves a video introduction (found below) of the concept of erosion, followed by a brief text and some definitions. The video is from one of my childhood favorites:

After watching the video, I have students discuss their definitions of erosion and write them down on the first page of the Notes & Video resource. After taking a few responses, we collectively jump into the text, which introduces some more information about erosion. We read this together, stopping to fill in the associated blanks [Note: Please see the embedded comments in the Microsoft Word document in the Lesson Introduction section above for the answers to those missing words and phrases] or answer some guiding questions that I pose to students. The text itself re-introduces the concept of dynamic equilibrium and also focuses on the varying types of mass movement, or erosion caused directly by gravity. 

When we get to the Agents of Erosion - Water section in the Notes & Video resource, I have students bust out their Earth Science Reference Tables [ESRT] (page 6!) and go to the Relationship of Transported Particle Size to Water Velocity graph, which we then begin to analyze. As noted above, the embedded comments should help here, but I try to hone in on a few aspects of this graph. At first glance, it appears complicated, but once students get the hang of it, it becomes relatively easy to use. 

For one, I make sure that students have the appropriate knowledge that the scales in this graph are logarithmic - they jump by factors of ten (10)(Note: You can also see my students explore logarithmic scales in this lesson on earthquakes). As the stream velocity increases (the x-axis), the particle diameter (the y-axis on the left hand side) that can be transported by the stream also increases, exemplifying a direct relationship, which is specifically represented by the thick black line running through the graph. In that sense, the opposite is also true. As stream velocity slows down, water can transport smaller and smaller sediments. This means, fundamentally, that water sorts sediment by size. Those sediments are also given specific names based on their size - for example, as represented by the right y-axis, anything with a particle diameter between 0.2 - 6.4 cm is classified as a pebble, while those over 25.6 cm are classified as boulders. The tick marks on the top and bottom of the graph represent values expressed logarithmically; the first tick mark after the 100 cm/s value, for instance, is 200 cm/s. I explicitly model this with the first Practice question on the bottom of the Notes & Video resource by showing them explicitly how I got an answer of cobbles (find 200 cm/s and follow it up to where it intersects the black line, then scroll to the right to find out what size sediment it can transport at that speed). 

Practice

20 minutes

The Practice section in this lesson is, like the vast majority of questions found in all of my classwork and homework, is 100% Regents-based. All of the questions come from prior Regents examinations. Likewise, as I try to generally do with all of my lessons, the questions are mostly organized to get increasingly more difficult and increase in complexity, which is why the harder questions tend to come toward the end. For whatever reason, the Regents loves to ask questions about source regions and air masses, so I truly think the practice is worthwhile, considering this is something they'll see over and over and over again in the future. 

In terms of student work habits, I tend to sometimes make this decision in the moment, and as a response of what I know about the students and how they're processing the material on, but I'll either ask them to work independently, in partners, or (sometimes) give them the option. Usually, before starting practice, we tend to go over some steps for self-help ("What should you do if you're stuck?"), and I might reference a previously used multiple-choice or free response strategy in order to build their skills while simultaneously learning content (as an example - one popular one we always use - "If you aren't sure what the right answer is, see if you can eliminate some wrong answer choices"). I tend to circulate for compliance and then hone in on specific students while they're doing this. 

After about 10 minutes, we go over their responses. Students who finish early are encouraged to work on the exit ticket (resource below) and double-check their responses. We use a combination of strategies (active voting, cold calling, popsicle sticks, volunteers) to go over the responses, where students correct their work and ask any clarifying questions. 

Exit Ticket

5 minutes

In the last few minutes of class, I have students complete the daily Exit Ticket. For the sake of time, I have students grade them communally, with a key emphasis on particular questions and items that hit on the key ideas of the lesson (Note: This usually manifests as students self-grading, or having students do a "trade and grade" with their table partners). After students grade their exit tickets, they usually pass them in (so that I can analyze them) and track their exit ticket scores on a unit Exit Ticket Tracker. 

After students take a few seconds to track their scores, we usually wrap up in a similar way. I give students time to pack up their belongings, and I end the class at the objective, which is posted on the whiteboard, and ask students two questions:

  • Do you feel that you mastered the objective for the day?
  • Can you reiterate one thing you learned about (in this case, the definition of erosion or the relationship between stream velocity and particle size, etc.)?

Once I take 2-3 individual responses (sometimes I'll ask for a binary "thumbs up/thumbs down" or something similar), I have students leave once the bell rings.