Miss Nelson

SCIENCE ~ CHAPTER 6

VOLCANOES

Volcanic Landforms

SECTION 3

When you picture a volcano, what shape is it?

Are all volcanoes shaped this way?

ANTICIPATORY SET

S 6.1.f –Students know how to explain major features of California geology in terms of plate tectonics

S 6.7.g – Interpret events by sequence and time from natural phenomena

STANDARDS

What landforms do lava and ash create?

How does magma that hardens beneath the surface create landforms?

THE BIG IDEA

Sheild volcano – a wide, gently sloping mountain made of layers of lava; formed by quiet eruptions

Cinder cone – a steep, cone-shaped hill or small mountain made of volcanic ash, cinders, and bombs

Composite volcano – a tall, cone-shaped mountain in which layers of lava and ash alternate

Caldera – the large hole at the top of a volcano formed when the roof of a magma chamber collapses

KEY TERMS

Volcanic neck – hardened magma in a volcano’s pipe

Dike – a slab of volcanic rock formed when magma forces itself across rock layers

Sill – a slab of volcanic rock formed when magma squeezes between layers of rock

Intrusion – an igneous rock layer formed when magma hardens beneath Earth’s surface

Batholith – a mass of rock formed when a large body of magma cools inside the crust

KEY TERMS

Read “Volcanic Landforms” on page 229 of your textbook

VOLCANIC ERUPTIONS

Volcanic eruptions create landforms made of lava, ash, and other materials

Include shield volcanoes, cinder cone volcanoes, composite volcanoes, and lava plateaus

LANDFORMS FROM LAVA AND ASH

At some places on Earth’s surface, thin layers of lava pour out of a vent and harden on top of previous layers

These gradually build a wide, gently sloping mountain called a shield volcano

Shield volcanoes created the Hawaiian Islands

SHIELD VOLCANOES

If a volcano’s lava is high in silica, it may produce:AshCindersBombs

These materials build up around the vent in a steep, cone-shaped hill or small mountain called a cinder cone

CINDER CONE VOLCANOES

Sometimes lava flows alternate with explosive eruptions of ash, cinder, and bombs

The result is a composite volcano

Tall, cone-shaped mountains in which layers of lava alternate with layers of ash

Examples: Mount Fuji in Japan Mount Shasta in California

COMPOSITE VOLCANOES

Some eruptions form high, level areas called lava plateaus

First, lava flows out of several long cracks or fissures

Then, thin/runny lava travels far before cooling and solidifying

This happens over and over again

After millions of years, these layers form high plateaus

LAVA PLATEAUS

The huge hole left by the collapse of a volcanic mountain is called a caldera Filled with pieces of volcano that have fallen inward, as

well as some lava and ash

Form when enormous eruptions empty the main vent and the magma chamber becomes a hollow shell With nothing to support it, the top of the mountain

collapses

View figure 13 on page 232 of your textbook

CALDERAS

People often settle close to volcanoes to take advantage of the fertile volcanic soil

Over time, the hard surface of the lava breaks down to form soilAs it breaks down, it releases potassium, phosphorus, and other substances that plants need

Some volcanic soils are among the richest soils in the world

SOILS FROM LAVA AND ASH

Sometimes magma forces its way through cracks in the upper crust, but fails to reach the surface

The magma cools and hardens into rock

Over time, the forces that wear away Earth’s surface (wind, flowing water, ice) may strip away the layers above the hardened magma and finally expose it

LANDFORMS FROM MAGMA

Features formed by magma include volcanic necks, dikes, sills, and batholiths

LANDFORMS FROM MAGMA

A volcanic neck looks like a giant tooth stuck in the ground

Forms when magma hardens in a volcano’s pipe

The softer rock around the pipe wears away, exposing the hard rock of the volcanic neck

VOLCANIC NECKS

Magma can force its way across or between rock layers

Magma that forces itself across rock layers hardens into a dike

When magma squeezes between horizontal layers of rock, it forms a sill

Dikes and sills are examples of igneous intrusions An intrusion is always younger than the rocks around it

DIKES AND SILLS

Form the core of many mountain ranges

Mass of rock formed when a large body of magma cools inside the crust

BATHOLITHS

What are the three main types of volcanoes?

What features form as a result of magma hardening beneath Earth’s surface?

CHECK FOR UNDERSTANDING

What are the three main types of volcanoes?The three main types of volcanoes are shield, cinder cone, and composite.

What features form as a result of magma hardening beneath Earth’s surface?The features that form as a result of magma hardening beneath Earth’s surface are volcanic necks, dikes, sills, and batholiths.

CHECK FOR UNDERSTANDING

What are two ways in which mountains can form as a result of magma hardening beneath Earth’s surface?

After millions of years, what landform forms from hardened magma in the pipe of an extinct volcano?

GUIDED PRACTICE

What are two ways in which mountains can form as a result of magma hardening beneath Earth’s surface?Mountains can form when uplift forces hardened magma to bend rock upward, and is then exposed as the hardened magma wears away.

After millions of years, what landform forms from hardened magma in the pipe of an extinct volcano?A landform that would form from hardened magma in the pipe of an extinct volcano after millions of years is a volcanic neck.

GUIDED PRACTICE

Complete Volcanoes 6-3 Independent Practice

INDEPENDENT PRACTICE