Volcanoes “Better put jam in your pockets, ‘cause we’re toast” --quote from a scientist running from the 1991 Mt. Pinatubo eruption

The Mercator projection

A projection of the surface of a sphere onto a cylinder

The Mercator projection Consider a small part of the surface near the equator

The Mercator projection The projection

The Mercator projection Consider a small part of the surface near the North pole

The Mercator projection

The projection

The Mercator projection The projection is much larger for polar regions!

The Mercator Projection Map

Alaska isn’t really as big as it looks!

Where are the volcanoes?

1)Mid-ocean ridges

Where are the volcanoes? 1)Mid-ocean ridges --in the middle of oceans (duh.) --North Pacific doesn’t have one.

Mid-Ocean Ridges

Where are the volcanoes? 1)Mid-ocean ridges 2)Edges of some continents

Where are the volcanoes? 1)Mid-ocean ridges 2)Edges of some continents --Only one edge each --Makes the Ring of Fire around the North Pacific

Edges of continents Ring of Fire

Where are the volcanoes? 1)Mid-ocean ridges 2)Edges of some continents 3)Hot spots

Where are the volcanoes? 1)Mid-ocean ridges 2)Edges of some continents 3)Hot spots --Hawaii, Yellowstone, Pitcairn Islands

Hot Spots

Older volcanoes show the plate has moved over the hot spot

Where are the volcanoes? 1)Mid-ocean ridges 2)Edges of some continents 3)Hot spots 4)Rifts

Where are the volcanoes? 1)Mid-ocean ridges 2)Edges of some continents 3)Hot spots 4)Rifts --New Mexico, East Africa

Rifts

Where are the volcanoes?

Topographic Maps

A topographic map has lines at certain elevations

Topographic Maps A topographic map has lines at certain elevations --They make loops around hills, but never cross. Downhill is at right angles to lines --Lines close together indicate steep slopes --Contour interval is the height difference between two lines --Relief is the difference from high to low on the map

Topographic Maps Steep slope— closely spaced lines

Topographic Maps Gentle slope— lines are not closely spaced

Topographic Maps Lines come together at a cliff

Lava flows downhill Magma contains:

Lava flows downhill Magma contains: --Melted rock --Dissolved gasses

Lava flows downhill Magma contains: --Melted rock --Dissolved gasses How much silica?

Lava flows downhill Magma contains: --Melted rock --Dissolved gasses High silica= high viscosity

Lava flows downhill Magma contains: --Melted rock --Dissolved gasses High viscosity = slow lava!

Lava flows downhill Magma contains: --Melted rock --Dissolved gasses Lots of gas= lots of pressure

Lava flows downhill Magma contains: --Melted rock --Dissolved gasses Lots of pressure  pyroclastic flows

Lava flows downhill Magma contains: --Melted rock --Dissolved gasses Lots of pressure  pyroclastic flows “hot”“chunks”

Lava flows downhill Magma contains: --Melted rock --Dissolved gasses Lahars might be even more dangerous— mudflows from melted snow on the volcano

Everything flows downhill Q: How far will it go?

Everything flows downhill Q: How far will it go? A: It depends…

Everything flows downhill Q: How far will it go? A: It depends… –Volume of material –Viscosity –Type of flow –Slope –Surface features

What can you do about it?

1)Be somewhere else.

What can you do about it? 1)Be somewhere else. 2)Maybe, if it’s a small flow…

What can you do about it? 1)Be somewhere else. 2)Maybe, if it’s a small flow a.Fireproof roofs—in case of pyroclastics b.Cool lava with fire hoses to solidify it c.Barriers could turn it aside d.Drainage channels to channel it around structure

Airborne Hazards How much gets tossed into the air? What gets tossed? How hard is it tossed?

How much gets tossed into the air? Measure the volume in cubic kilometers! (km 3 )

How much gets tossed into the air? There is a huge variation in volume Small: up to 1 km 3 Medium: up to 10 km 3 Large: up to 100 km 3 Gigantic: hundreds of km 3

What gets tossed? Sizes of particles Tephra—general term for airborne pieces Volcanic bombs Lapilli Ash

What gets tossed? Sizes of particles Tephra—general term for airborne pieces Volcanic bombs—largest chunks (>fist-sized) Lapilli—smaller chunks Ash—smallest particles (< 2mm, dust-sized)

What gets tossed? Distance Different sizes of particles go different distances The smaller the particle, the farther it goes Volcanic bombs < Lapilli < Ash

What gets tossed? Damage Volcanic bombs—dangerous only if it hits you. Lapilli—dangerous only if it hits you Ash—damages lungs, motors, smooth surfaces, forms lahars

How hard is it tossed? Measured against the VEI —the Volcanic Explosivity Index

How hard is it tossed? Measured against the VEI —the Volcanic Explosivity Index Ranges from: 0 (mild) to 7 (We’re all going to die!)

How hard is it tossed? VEI is related to volume VolumeVEI Small: up to 1 km Medium: up to 10 km 3 5 Large: up to 100 km 3 6 Gigantic: hundreds of km 3 7

How hard is it tossed? VEI is related to the type of magma The higher the silica and dissolved gasses, the higher the VEI

How many are killed? How much gets tossed into the air? What gets tossed? How hard is it tossed? How many people live in the path of the flows and airborne debris?