Notes-Volcano Notes for Weebly

8/14/2019 Notes-Volcano Notes for Weebly

1/42

Volcanoes


2/42

BIG Questions

1 What plate settings dovolcanoes occur at?2 - Volcanoes arent equallydangerous....how do their hazards differ, andwhy?

VOLCANOES


3/42

Volcano

an opening in a planet'scrust, which allows hot molten rock,

ash, and gases to escape from

below the surface.


4/42

What comes out of a volcano?Ash


5/42

What comes out of a volcano?GasMost common:

H2OCO2SO2HCl


6/42

What comes out of a volcano?

Lava


7/42

So...Why are there differenttypes of Volcanoes

Viscosity of the magma controls the type ofvolcano.

Viscosity a liquids resistance to flowLow viscosity flows easilyHigh viscosity flows slowly

Viscosity is controlled by the compositionand temperature of the magma.

Silica (SiO2) content controls viscosity.


8/42

BasalticAndesitic

Rhyolitic


9/42

Composition

MagmaSource

Viscosity Gas % Silica % Explosiveness

Location

Basaltic UpperMantle

Low 1-2 % ~ 50 % Least /Mild

DivergentBoundaries and HotSpots

Andesitic OceanCrust &Sediments

Medium -High

3-4 % ~ 60 % Intermediate

Convergent

Subduction Zones

Rhyolitic Continent

al Crust

High -

Extreme

4-6 % ~ 70 % Greatest Convergen

tSubduction Zones

High silica = high viscosity = explosive eruption

Low silica = low viscosity = quiet eruption

Viscosity and Silicacontent


10/42

Shape

Shapes of volcanoes are due to theviscosity of the magma.

Runny lava forms relatively flat shieldvolcanoes with quite eruptions.Thick lava forms steep cones with explosive

eruptions.


11/42

Explosivenes

Explosiveness of the volcano

is controlled by

- the silica content of the magma

- the viscosity of the magma

- the release of gases


12/42

Types of Eruptions

Explosive cloggedPlate Setting: Convergent Boundary Subduction Zones

Type of Volcano: Composite volcanoes and Cinder Cones

Type of Magma: Andesitic or Rhyolitic composition

Quiet runny

Plate Setting: Divergent Boundariesand Hot Spots

Type of Volcano: Shield volcanoes

Type of Magma: Basaltic composition


13/42

Quiet Eruptions

Magma flows easilyGasses bubble out gently


14/42

Plate Setting: Divergent Boundary

ivergent boundary volcanoes have very low viscous magma

and non-explosive eruptions


15/42

Plate Setting: Hot Spot

Hot spot volcanoes form when mantle plumes rise

through the crust like a blow torchCharacterized by low viscous magma and non-explosive

eruptions


16/42

Type of Volcano:

Shield

Usually start under water

resembles a Roman shield lying on the ground

characterized by relatively quiet eruptions with lavaflows that harden on top of each other


17/42

Examples:- Hawaiian Islands- Iceland

Type of Magma: Basaltic

runny, low viscosity lava

relatively little explosiveactivity


18/42

ilauea, Hawaii: A typical shield volcan


19/42

Basaltic eruptions produce 2 types of lava

oehoe hot, fast moving lava. Surface looks lwrinkles and rope-like coils


20/42

Pahoehoe Lava


21/42

Pahoehoe Lava


22/42

Basaltic eruptions produce 2 types of lava

cooler, slow moving lava. Hardens to form roujagged lava chunks


23/42

Anatomy of a Shield Volcano


24/42

Explosive Eruptions

Magma is thick and sticky

Magma slowly builds up in the volcano's pipe

Gasses cannot easily escape from the magma

Trapped gasses build up pressure until thevolcano explodes

More dangerous and have more hazards such aspyroclastic flows

Pyroclastic Flows


25/42

Pyroclastic Flows

Pyroclastic flows - fast-moving hotgas and rock fragments which travelaway from the volcano

speeds generally as great as 450miles/hr

Can reach temperatures of 1,830 F


26/42

Plate Setting: Convergent Boundary

Explosive volcanoes form atconvergentsubduction zones and have highly viscous

magma


27/42


28/42

Type of Volcano: Cinder Cone

relatively small (less than 300 m or 1000 ft high) relatively steep slopes (30 - 40 degrees)

made of pyroclastic material


29/42

Type Of Magma: Andesitic

- high silica content- highly viscous magma- explosive eruptions

Examples- Paracutin, in Mexico


30/42

Anatomy of a Cinder Cone


31/42

ype of Volcano: Composite

large (1 - 10 km across) Also called a Stratovolcano layered structure, consisting of alternating

layers of lava and pyroclastic material

These volcanoes make up the largestpercentage of the Earth's volcanoes (about

60%)


32/42

Type Of Magma: Rhyolitic- high silica content- highly viscous

- explosive eruptions

Examples:Mt. Vesuvius,

Mt. St. Helens andMt. Rainier in the Cascade

Range


33/42

Mt. St. Helens: Before the 1980 eruption


34/42

Mt. St. Helens after its 1980 eruption


35/42

Anatomy of a Composite Volcano

Pyroclasticflow


36/42

Status of a Volcano

Active currently erupting orshowing signs of an imminent

eruption. Risk is high

Dormant does not show signs of anerupting in the near future or hasnot erupted in the recent past

Extinct unlikely to ever eruptagain


37/42

Signs a volcano is about toerupt

When a volcano begins to show new orunusual signs of activity, it ispossible it is about to erupt

Increased Earthquake Activity

Ground Deformation

Change in water composition

Gas emissions

Monitoring from space


38/42

Volcanic Hazards


39/42

Volcanic Hazards

Lava flows

Ash fall

Pyroclastic flows

Mudflows

Volcanic Gases

Tsunami

l i d


40/42

Volcanic Hazards

V l i H d


41/42

Volcanic Hazards


42/42

Volcanic Hazards

Volcano Hazards program

http://volcanoes.usgs.gov/activity/alertsystem/icons.php
http://volcanoes.usgs.gov/activity/alertsystem/icons.phphttp://volcanoes.usgs.gov/activity/alertsystem/icons.php

Documents

Notes-Volcano Notes for Weebly