NGS - Forces that Shape the Earth Sec. 1

What is stress in the context of geology?

• A force that acts on a rock to change its shape or volume

• A type of rock formation

• A weather phenomenon

• A type of mineral

Answer explanation

Imagine you have a block of clay.

• Stress in geology is like pushing, pulling, or twisting that block of clay. It's a force that can change the shape or volume of the rock.

• Strain is what happens to the clay when you apply stress. It might bend, break, or squish.

Now, think about the Earth's crust.

• It's made up of giant pieces called tectonic plates that are constantly moving.

• When these plates collide, pull apart, or slide past each other, they create stress on the rocks.

• This stress can cause mountains to form, earthquakes to happen, and volcanoes to erupt.

So, the answer is:

• A force that acts on a rock to change its shape or volume

Here's a cool way to remember it:

• Stress is like a push or pull on a rock.

• Strain is how the rock reacts to that push or pull.

Bonus:

• There are different types of stress, just like there are different ways to push or pull on the clay.

• Geologists study stress and strain to understand how the Earth's surface changes over time.

Which type of stress pulls on the crust, making it thinner in the middle?

• Shearing

• Tension

• Bending

• Compression

Answer explanation

Imagine you have a piece of gum. You can do a few things to it, right?

• Shearing: Think of this like sliding the top of the gum in one direction and the bottom in the opposite direction. It's like what happens when tectonic plates slide past each other. This doesn't necessarily make the gum thinner in the middle, more like shifted.

• Tension: This is like pulling on the ends of the gum. If you pull hard enough, what happens in the middle? It gets thinner! This is exactly what happens to the Earth's crust when it's under tensional stress. It stretches and thins.

• Bending: Imagine bending the gum. One side gets squished together (compressed), and the other side gets stretched (tensed). While this changes the shape, it doesn't thin the middle in the same way as tension.

• Compression: This is like squishing the gum from the top and bottom. It makes it wider and shorter, not thinner in the middle.

So, the answer is Tension!

Think of it like this: Tension is like a tug-of-war. When the Earth's crust is pulled apart, it stretches and thins, just like the gum. This is how valleys and other features can form.

What landform is created by the collision of two continental plates?

• Mid-ocean ridge

• Mountain range

• Ocean trench

• Volcanic arc

Answer explanation

Alright, let's talk about what happens when two giant landmasses crash into each other! Imagine two enormous rafts, each made of land (continents), floating on a giant, slow-moving lake (the Earth's mantle).

• Mid-ocean ridge: This is like a crack in the "lake" where new "raft" material is rising up. It happens when plates are pulling apart, not colliding.

• Mountain range: Now, imagine those two land rafts bumping into each other. What happens when two big globs of clay collide? They squish upwards! That's exactly how mountain ranges are formed. The immense pressure forces the land upwards, creating towering peaks. Think of the Himalayas, formed when India crashed into Asia!

• Ocean trench: These are deep canyons in the ocean floor. They form when one plate slides under another (subduction), usually an ocean plate going under a continental plate. This isn't what happens when two continents collide.

• Volcanic arc: These are chains of volcanoes that often form near ocean trenches where subduction is happening. Again, not the result of two continents colliding directly.

So, the answer is Mountain range!

Think of it like this: Continent vs. Continent = Mountain! It's a head-on collision, and the land has nowhere to go but up!

How do ocean trenches form?

• By the sliding of plates past each other

• By the spreading of oceanic crust

• As one plate goes under another plate

• By the collision of two oceanic plates

Answer explanation

Let's dive into the ocean and see how these giant trenches are made! Imagine the Earth's crust as a giant puzzle made of pieces called plates. Some are land (continents), and some are ocean (oceanic plates).

• By the sliding of plates past each other: Think of this like two boats sliding past each other. This is called a transform fault, and while it can cause earthquakes, it doesn't create deep trenches.

• By the spreading of oceanic crust: This is how mid-ocean ridges are formed, like a zipper opening up on the ocean floor. New crust is created, pushing the plates apart.

  This is the opposite of what happens at a trench.

• As one plate goes under another plate: This is the key! Imagine one oceanic plate, which is denser, bending and sliding under another plate (which can be either oceanic or continental). It's like diving under a blanket. This "under" part creates a deep, deep gash in the ocean floor – a trench! This process is called subduction.

• By the collision of two oceanic plates: While two oceanic plates can collide, this usually results in volcanic island arcs and less so a long, deep trench. The subduction of one plate beneath the other is what primarily forms trenches.

So, the answer is: As one plate goes under another plate!

Think of it like this: One plate dives under another, creating a super deep "valley" in the ocean floor. These trenches are the deepest parts of the ocean!

What is a transform fault?

• A fault where plates subduct

• A fault where plates collide

• A fault where plates move apart

• A fault where plates slide horizontally past each other

Answer explanation

Alright, let's talk about a type of fault that's all about sideways movement! Imagine you have two giant LEGO bricks, representing Earth's plates.

• A fault where plates subduct: This is where one brick slides under the other, like we talked about with ocean trenches. That's not a transform fault.

• A fault where plates collide: This is where the bricks smash into each other, creating mountains. Again, not a transform fault.

• A fault where plates move apart: This is where the bricks are pulled away from each other, like at a mid-ocean ridge. Not a transform fault either.  

• A fault where plates slide horizontally past each other: This is it! Imagine sliding those LEGO bricks past each other, side by side. That's exactly what happens at a transform fault. They grind against each other, causing earthquakes but not creating mountains or trenches in the same way other faults do. Think of the San Andreas Fault – it's a famous example of a transform fault.  

So, the answer is: A fault where plates slide horizontally past each other!

Think of it like this: Transform faults are like a sideways shuffle. The plates are just sliding past each other, not colliding or diving under each other.  

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Now, for a special message to anyone reading this: If you've made it this far, you're awesome! I'm curious to know if anyone actually reads these explanations. If you do, when you submit your answer to Google Classroom, please also include the code "GeoRocks" in the submission notes. This will let me know you're one of the dedicated learners! Remember to keep it a secret, if too people find out without reading this, it will end this experiment in house points. Thanks!

What type of strain is NOT permanent?

• Ductile strain

• Elastic strain

• Plastic strain

• Brittle strain

Answer explanation

Alright, let's talk about how rocks react when you squish, pull, or twist them! Imagine you have a few different materials: silly putty, a rubber band, and a cracker.

• Ductile strain: This is like silly putty. You can stretch it, bend it, and mold it, and it stays in the new shape. It's a permanent change.

• Elastic strain: This is like a rubber band. You can stretch it, but when you let go, it snaps back to its original shape. The change is temporary – it's NOT permanent.

• Plastic strain: This is also like silly putty! It can be molded and stay in the new form after the stress is removed. It's a permanent change.

• Brittle strain: Imagine bending a cracker. Snap! It breaks. This is a permanent change too, because the cracker is now in pieces.

So, the answer is Elastic strain!

Think of it this way: Elastic strain is like a spring. You stretch it, but it bounces back. The other types of strain are like clay – you mold them, and they stay that way. Elastic strain is the only one that's not a lasting change.

Which landform is created by tension in the Earth's crust?

• Volcanic arc

• Mountain range

• Ocean trench

• Mid-ocean ridge

Answer explanation

Hey there, Earth explorers! Let's groove on down to learn about landforms created by tension in the Earth's crust. Imagine the Earth's crust like a giant, cosmic dance floor, and the plates are the dancers.

• Volcanic arc: These are chains of volcanoes, often near ocean trenches. They're more about one plate diving under another, not just tension. Think of them as the fiery spotlights on the dance floor.

• Mountain range: These are formed by compression, like two dancers bumping into each other and pushing upwards. Not tension, which is more like pulling apart.

• Ocean trench: These are deep canyons in the ocean, formed by one plate sliding under another. Again, not directly caused by tension alone.

• Mid-ocean ridge: This is our groovy landform! Imagine two dancers moving away from each other, creating a space in the middle. That's what happens at a mid-ocean ridge! Tension pulls the plates apart, and magma rises up to fill the gap, creating new oceanic crust. It's like a zipper opening up on the ocean floor.

So, the answer is Mid-ocean ridge!

Think of it like this: Tension is like stretching a rubber band. When the Earth's crust is pulled apart, it creates these underwater mountain ranges called mid-ocean ridges. It's where new crust is born! Far out!

What is a fault zone?

• A region with no tectonic activity

• A type of volcanic region

• A single break in the Earth's crust

• An area with many fractured pieces of crust along a large fault

Answer explanation

Okay, buckle up, buttercup, because we're about to talk about fault zones! Imagine the Earth's crust as a giant chocolate bar. Sometimes, when it gets stressed (like when you try to snap it), it doesn't just break in one clean line. Oh no, it gets complicated.

• A region with no tectonic activity: That's like saying your chocolate bar never gets touched. Faults are all about tectonic activity, so this is the opposite of what we're looking for.

• A type of volcanic region: Volcanoes are awesome, but they're not directly the same thing as a fault zone. Think of it like chocolate and marshmallows – both delicious, but different things.

• A single break in the Earth's crust: That's like a clean snap of the chocolate bar. A fault zone is much messier!

• An area with many fractured pieces of crust along a large fault: THIS is our chocolate bar after a toddler got hold of it! It's not just one break; it's a whole zone of cracks, crumbles, and fractured pieces. That's a fault zone! It's not just one fault line; it's a whole bunch of them, all tangled up together.

So, the answer is: An area with many fractured pieces of crust along a large fault!

Now, I know what you're thinking. "Wow, that's the longest answer! That must be the right one!" And you're right! But not just because it's long. It's the right answer because it accurately describes a fault zone. It's like, the longer the explanation of why your room is messy, the more likely it actually is messy. Just kidding (mostly)! Fault zones are complex, and this answer reflects that complexity. They're not just single cracks; they're zones of broken-up rock. Got it? Good! Now go clean your room...I mean, study some geology!

What type of landform is a volcanic arc?

• A single isolated volcano

• A cluster of volcanoes at a divergent boundary

• A straight line of volcanoes

• A curved line of volcanoes parallel to plate boundaries

Answer explanation

Alright, volcano fans, let's talk about volcanic arcs! Imagine the Earth's crust like a giant puzzle, and the pieces are constantly moving (very, very slowly!).

• A single isolated volcano: While volcanoes can exist on their own, a volcanic arc is more like a family of volcanoes. It's not a lonely volcano; it's a whole crew!

• A cluster of volcanoes at a divergent boundary: Divergent boundaries are where plates are pulling apart. While volcanoes can form there, they're usually more spread out and don't form the distinct arc shape we're talking about. Think of it like a few scattered campfires, not a campfire circle.

• A straight line of volcanoes: Volcanic arcs are rarely perfectly straight. They usually have a curve to them.

• A curved line of volcanoes parallel to plate boundaries: THIS is our winner! Volcanic arcs are typically curved lines of volcanoes, and they often form parallel to the edges of tectonic plates, especially at subduction zones (where one plate slides under another). Think of it like a curved string of lights along the edge of a stage.

So, the answer is: A curved line of volcanoes parallel to plate boundaries!

Think of it like this: A volcanic arc is like a curved necklace of volcanoes. They're all related and formed by the same tectonic activity, usually at a place where one plate is diving beneath another.

This subduction creates the magma that feeds the volcanoes. They're not random; they follow the curve of the plate boundary.

What happens during compression stress?

• Rock is melted and reformed

• Rock is pushed in two opposite directions

• Rock is squeezed until it folds or breaks

• Rock is stretched and thinned

Answer explanation

Yo, young scholars, let's break down compression, word. Imagine the Earth's crust, a canvas, you heard? Different forces actin' on it, a cosmic tug-of-war.

• Rock is melted and reformed: Nah, that's more like a volcanic eruption, a fiery transformation. Compression ain't about meltin', it's about pressure, feel me?

• Rock is pushed in two opposite directions: While forces are involved, it's more than just a push. It's a squeeze, a tighten, a real pressure cooker.

• Rock is squeezed until it folds or breaks: THIS. This is the truth, the real deal. Compression's like a giant hand, squeezin' the rock, makin' it bend, fold, maybe even crack. Think mountains risin', that's compression's action.

• Rock is stretched and thinned: That's tension, the opposite of compression. Think of pullin' taffy, makin' it long and lean. Compression's the opposite, makin' it short and mean.

So, the answer, the real answer, the one you gotta know: Rock is squeezed until it folds or breaks. Compression's the pressure, the force, the squeeze. It's the Earth's way of changin' the game, rearrangin' the scene. Word.