Let’s Review Our Homework
2) Compare and contrast quiet and explosive eruptions
Quiet eruptions occur if the magma is thing and runny. The gases
dissolved in the magma bubble out gently , and the lava oozes from the
vent. Explosive eruptions occur if the magma is thick and sticky. The
magma slowly collects in the volcano’s neck and plugs it, trapping the
gases. Pressure builds up until the gases explode, pushing the magma out
of the volcano with great force.
4) A geologist times a passing lava flow at 15 km/hr. The geologist also sees
the lava near the edge of the flow is forming smooth-looking ripples as it
hardens. What type of lava is this? What type of magma produced it?
Explain your conclusions.
Pahoehoe; produced by thin lava. The speed is high, and smooth ripples
are characteristic of pahoehoe.
What are the
different kinds
of volcanoes?
Volcanoes do not all look alike. Their
shape is based on what type of
materials they erupt. There are three
main kinds, or shapes, of volcanoes.
Shield
Volcanoes
Volcanoes that build up from
many slow, steady, flows of hot
lava, are called shield volcanoes.
This kind of volcano is low and
broad with gently sloping sides.
They look like a warriors shield.
Cinder Cone
Volcanoes
Cinder cone volcanoes form when
solid rock and ash shoot up into
the air and fall back around the
volcano opening. The cinder cone
volcano has steeply sloped sides.
Strato
or Composite
Volcanoes
Strato volcanoes, also called
composite volcanoes, erupt with
molten lava, solid rock, and ash.
The layers pile up much like layers
of cake and frosting. The layers
form into symmetrical cones, and
the slopes are steep.
There is much more about volcanoes out
there. Look in books and on the
internet . Have Fun!
Pictures, Images, and information From:
Soames Summerhays/Photo Researchers, Inc.
Kraft-Explorer/Photo Researchers Inc.
Masao Hayashi-Dung/Photo Researchers Inc.
Why Do Volcanoes Blow Their Tops? By Melvin and Gilda
Berger
www.usgs.gov/education/learnweb/volcano/index.html
E. Landforms from Magma
…Magma does not always reach the surface. As a
result features such as volcanic necks, dikes, and sills,
as well as batholiths and dome mountains form!
E. Landforms from Magma
1. Volcanic Neck
a. Forms when magma hardens in a volcano’s pipe
2. Dike
1. Magma that forces itself across rock layers vertically
3. Sill
1. Magma squeezes between layers of rock horizontally
Sill
E. Landforms from Magma (Continued)
4. Batholiths
a. A mass of rock formed when a large body of magma
cools inside the crust
b. Form the core of many mountain ranges
5. Dome Mountains
4. Form when rising magma is blocked by horizontal
layers of rock
5. The magma forces the layers of rock to bend upward
into a dome shape
E. Landforms from Magma (Continued)
6. Soils from Lava and Ash
a. Volcanic soils are among the richest in the world
b. Volcanic ash breaks down and releases plant
nutrients
c. Part of the reason why people settle near
volcanoes
HOMEWORK
• Read Section 3, pages 193-197
• Index cards for bold vocabulary words found
in Section 3
• Section 3 Review, questions 3 and 5
• Complete your brochure for tomorrow