Volcano Lecture2015

8/19/2019 Volcano Lecture2015

1/28

Volcanism

• Volcanic Features

• Location and Types of Volcanic Activity

• Effusive Eruptions

• Explosive Eruptions

• Volcano Forecasting and Planning


2/28

Volcanoes

Volcanic activity takes place primarily at subduction

boundaries,

VOCABULARY

How and Where Volcanoes Form

Oceanic

lithosphere

Continental

lithosphere

Asthenosphere

1. Water in the suducted roc! is

released into the asthenosphere.

". #he water lowers the meltin$ temperatures o%

materials in the asthenosphere& leadin$ to ma$ma

%ormation.

'. #he ma$ma

is less dense

than its

surroundin$s&

so it rises.

(. )ome o% the ma$ma reaches

*arth+s sur%ace& and ,olcanoes

%orm on the o,erridin$ continentalplate.

,olcano

hot spot


3/28

#he Hawaiian -slands %ormed o,er a hot spot.

Volcanoes

Magma and volcanoes also form at

hot spots.

VOCABULARY How and Where Volcanoes Form

irection o%

/late

0o,ement

auai

Oahu0olo!ai

Lanai

0aui

Hawaii

,olcano

hot spot


4/28

How Magma Rises

http://../Animations/MagmaRiseppt.htmlhttp://../Animations/MagmaRiseppt.html


5/28

Volcanic Settings


6/28

Plate Tectonics and Magma eneration

http://../Earth%20Sci%20ppt%20and%20images/volcanoes/Present/Animations/MagmaMeltingppt.htmlhttp://../Earth%20Sci%20ppt%20and%20images/volcanoes/Present/Animations/MagmaMeltingppt.html


7/28

Major Volcanoes Around theWorld


8/28

Gases escape easily from basaltic magma,generating relatively quiet eruptions.

Hardened basaltic lava o!s on land are

characteri"ed as pahoehoe or aa# if the lava

cools under!ater, it is characteri"ed as pillo!

lava.

Magma and !rupted Materials

A.Parameters of volcanism:

1.Viscosity

2.Chemistry of Magma3.Gases within the magma

4.Water content of magma


9/28

VOCABULARY

,iscosit2la,a

pahoehoe

aa

pillow la,ap2roclastic material

p2roclastic %low

0a$ma and *rupted 0aterials

Viscosity: Viscosity is a

measure of how thick (viscous)

and sticky a liquid is.

Magma and !rupted Materials


10/28

Lava Flows• Lava Flow - A

'stream' of moltenrock

• 'aa' lava flow - jagged,

rubbly, broken

surface

• 'pahoehoe' lava flow -smooth, ropy surface


11/28

)ilica Content

0eltin$ #emp.

3as Content

Viscosit2

#2pe o%*ruption

Location

Least 456789

Basaltic

0a$ma

Least

Least ,iscous

Rarel2e:plosi,e

Hi$hest

Ri%ts& oceanic

hot spots

Andesitic0a$ma

-ntermediate 45;789

-ntermediate

-ntermediate

)ometimes e:plosi,e

-ntermediate

)uduction

oundaries

Rh2olitic

0a$ma0ost 45


12/28

Volcanic Landforms

" volcano#s shape and structure depend on how it erupts and

what materials are released. $hield volcanoes are formed by

basaltic lava that flows long distances before hardening.


13/28

Tectonic $ettings and Volcanic "ctivity


14/28

Igneous __________- classified by

shape, size, and orientation

$ntrusions


15/28

There are three types of volcanic

cones:

• ______ – explosive eruptions, small but

steep slopes, pyroclastics.• _______ – non-explosive eruptions, fluid

basaltic lava, gentle broad slopes.

• _________ – alternating between lava andpyroclastics, explosive and non-explosive

eruptions, steep and tall.

%inde

r&hield

%omposite


16/28

Volcano Types


17/28

Volcanoes

" volcano#s shape and structure depend on how it

erupts and what materials are released.

VOCABULARY

Volcanic Land%orms

$hield volcanoes are formed by basaltic lava that

flows long distances before hardening.

)hield

Volcano

shield ,olcano

cinder cone

composite ,olcano

lahar

caldera

la,a plateau


18/28

Shield and Composite Volcanoes


19/28

Volcanoes

%inder cones are formed when molten lava is thrown into the air from a

vent and breaks into drops. These drops harden into cinders that form a

steep cone around the vent.

Volcanic Land%orms

Cinder Cone


20/28

Volcanoes

%omposite volcanoes are formed by layers of

pyroclastic materials and lava that have erupted in

the past.

Volcanic Land%orms

CompositeVolcano


21/28

%omposite volcanoes


22/28

&ebris "valanche and !ruption of Mount $t. Helens,

'ashington


23/28

Nuee ardente: yroclastic flow! of searing s"erheate#

gas an# incan#escent volcanic ash an# #"st

Mo"nt Pelee! on the Carri$ean islan# of Martini%"e! 1&'2 er"tion. All $"t 2 of the more than2'!''' eole in the town of (t. Pierre were )ille#.


24/28

Volcanoes Volcanic Land%orms

" caldera is a large crater(shaped basin that

forms when the top of a volcano collapses.


25/28

)ormation of %rater *ake


26/28

EFFUSIVE ERUPTIONS

• Generally at hots spots, spreading centers

•Mantly comes directly to surface

• Hot lava; low viscosity, very mafic, flows

easily, gases escape easily

• Forms shields, flood basalts


27/28

EXPLOSIVE ERUPTIONS

• Found at subduction zones

• Magma low temp (800 degrees C), high

viscosity, does not flow easilty, more felsicmineralogy, gases trapped, hard to predictexplosions

• Forms composite volcanoes, cinder cones,calderas, aerial bombs, nuee ardente gasflows, very destructive


28/28

Documents

Volcano Lecture2015