New Unit- Rapid Changes to Earth's Surface

Student Expectation

The student is expected to investigate rapid changes in Earth’s surface, such as volcanic eruptions, earthquakes, and landslides.

Key Concepts

• Large forces can change the Earth’s surface rapidly.
• Volcanic eruptions and earthquakes can cause rapid changes on Earth’s surface such as creating new land, making cracks in the crust, or changing landforms.
• Landslides can cause rapid change to Earth’s surface such as rocks and debris falling from a rock face.

Fundamental Questions

• What are some forces that can cause rapid changes to the Earth’s surface?
• What are the effects of rapid changes to the Earth’s surface?

Key Concept 1: Large forces can change the Earth’s surface rapidly.

Most features on Earth’s surface, such as mountains, valleys, and plains, are created over hundreds or thousands of years. However, some events, such as volcanic eruptions, earthquakes, and landslides, occur very rapidly and can completely change the surface within just hours or days. These slow and rapid changes create different landforms because of natural forces that work above and below the ground. Earth is made of three basic layers: the crust, the mantle, and the core. The crust and the rigid upper part of the mantle move together on top of soft molten rock deeper in the mantle (caused by tremendous internal heat of Earth).

Instead of one giant layer, the crust and upper mantle move very slowly together as broken puzzle pieces called plates. This slow movement is caused by the molten rock beneath sliding past the enormous plates above. Two of the three large forces that change the surface rapidly, volcanoes and earthquakes, begin below the surface of Earth along boundaries where these plates collide. The third large force, landslides, occurs above the surface.

Key Concept 2: Volcanic eruptions and earthquakes can cause rapid changes on Earths surface, such as creating new land, making cracks in the crust, or changing landforms.

Volcanic eruptions and earthquakes are natures pressure valves. Along plates bordering the Pacific Ocean, magma (molten rock) is forced up through cracks to the surface releasing pressure in volcanic eruptions. Numerous volcanoes and earthquakes occur along this Pacific Ring of Fire.

Volcanoes erupt when magma reaches the surface as lava. Lava flows down the sides of the volcano and hardens. Ash, cinders, and gases are also released. The largest volcanoes release slow, continuous lava flows to create wide, volcanic mountains. Some volcanoes erupt violently with pyroclastic flow (deadly avalanche of superheated fragments, ash, and gas) that destroys landscape and lives in its path. Some volcanoes form on the ocean floor over hot spots, and after repeated eruptions, build up enough lava to form islands like the Hawaiian Islands. Volcanoes both destroy and create landscape.

When volcanic lava rock erodes after many years, soil often collects in the crevices, allowing plant growth to take root and animal life to develop. Many volcanoes are no longer active, such as those that formed the Davis Mountains in Texas, but serve as reminders of how the very forces that destroy are the same forces that can create new land and new life.

When rough blocks of rock along plate boundaries move against each other and get stuck, pressure builds. Finally, the blocks move, which suddenly releases energy in the form of shaking vibrations called earthquakes that radiate outward like ripples in a pond. These vibrations, or seismic waves, are felt many miles away in two ways. The first set stretches the rock in a back-and-forth motion. The second set produces side-to-side shaking. Together, these vibrations can create massive damage to landforms, buildings, roads, bridges, power lines, and take the lives of the people and animals caught in the collapse. If the earthquake occurs on the ocean floor, the vibrations can cause enormous waves called tsunamis that crash into coastal areas, destroying and flooding miles inland.

Landslides occur where the earth collapses suddenly. This can be caused by seismic vibrations or when the earth has become too saturated with water and slumps downward. Landslides and other inevitable rapid changes to Earths surface have led to a special interest in creating infrastructures (building, roads, etc.) that can withstand these strong forces of nature.

Student Expectation

The student is expected to identify and compare different landforms, including mountains, hills, valleys, and plains.

Key Concepts

• A landform is a natural geographic structure on the Earth’s surface.
• Landforms, including mountains, hills, valleys, and plains, have specific characteristics.
• Landforms can look very different but can be formed by similar processes.
• We can compare different landforms based on their characteristics.

Fundamental Questions

• What is a landform?
• What are examples of landforms and the processes that created them?
• What are some characteristics we can use to compare landforms?

Every region on Earth has a unique combination of local landforms that make that area distinct. The landforms can include volcanoes, dunes, arches, cliffs, caves, reefs, beaches, plateaus, deserts, and peninsulas, but third grade students will focus on four landforms, mountains, hills, valleys, and plains, formed from incredibly slow forces that change the surface Earth.

Key Concept 1: A landform is a natural geographic structure on Earth’s surface.

Earth is constantly changing from forces that act above and below its surface. Students have explored rapid changes to geography, such as earthquakes, volcanoes and landslides, but the landforms in this Key Concept were all formed slowly over a long period of Earth’s geologic history. The forces that formed mountains, hills, valleys, and plains took millions of years to sculpt the surface of the Earth, which is still changing today.

Key Concept 2: Landforms, including mountains, hills, valleys, and plains, have specific characteristics.

Features on Earth range in elevation from the highest mountains, which tower over lower hills, down to the sea level plains. Valleys also range in elevation from glacier-formed U-shaped valleys in the highest mountains and young river-formed V-shaped valleys between mountains, down to flat, older sea-level river valleys.
Mountains are very large rock formations with a peak at the top. Generally, mountains are structures taller than 1000 feet high and many form in rows called ranges. Some peaks are so high they reach into the clouds and are covered in snow. In West Texas, the Guadalupe Mountains have the tallest peak in the state. The Rocky Mountains in the West and the Appalachian Mountains in the East are two major mountain ranges in the United States.

Hills are large land formations of rocks, dirt, and grass that have a rounded top. Hills are smaller than mountains with elevations generally lower than 1000 feet and do not have jagged peak tops. The Texas Hill Country is an example of the limestone, rolling hills that are part of Central Texas. Mounds that are higher than the surrounding flat area are also considered hills but are the lowest type of hill.

Valleys are the areas between two mountains or two hills. A low area of land between mountains or hills often has a river or stream running along the valley bottom. Rapid, young rivers cut through mountains leaving a V-shaped valley. In some alpine mountains, glaciers gouge out the sides of mountains leaving a U-shaped valley. Older rivers can run down the middle of flood plains, such as the Rio Grande Valley or the Red River Valley in Texas. Valleys also run among the Texas Hill Country formations.

A plain is a large, flat area of land with no mountains, hills, or valleys. The Great Plains in the United States span from the Mississippi River to the Rocky Mountains where broad, flat areas stretch for thousands of miles offering prime farmland. Texas plains are in the Panhandle and along coastal areas.

Key Concept 3: Landforms can look very different, but can be formed by similar processes.

Mountains form from slow-acting forces deep within Earth that push sections of the crust upward over millions of years into folded or block mountains. The Rocky Mountains were uplifted over 200 million years ago. The Guadalupe Mountains were formed by uplift 25 million years ago. Once mountains have formed, usually river water that collects and starts to flow downward begins to weather and erode the mountainsides into V-shaped valleys. Glaciers in alpine areas can weather and erode mountainsides into a U-shaped valley.
After hundreds of thousands of years, the constant erosion wears down the sides of the mountain, and rivers slow down leaving deposits in wide valleys on either side. The broad valleys of older rivers, such as the Mississippi or Rio Grande, are the results of eons of erosion and deposition. Hills also are folded parts of Earths crust, but represent mountain tops that have been eroded slowly over a long period of time leaving behind the mounds or hills as remnants of former tall peaks. The Great Plains were formed from uplift after an ancient sea that covered central North America long ago evaporated. So, uplift, weathering, erosion, and deposition are three common processes that change Earths surface dramatically, but the resulting landforms can look very different.

Key Concept 4: We can compare different landforms based on their characteristics.

Students are challenged to compare mountains, hills, valleys, and plains based on the characteristics summarized above. Below is a reference table that offers some basic comparisons students might propose: