Volcanoes Unit

a’a

a’a

is lava with a rough, jagged surface composed of broken lava blocks called clinkers, ---lava forms when lava has cooled, and its viscosity has been increased.

andesitic magma

higher viscosity and lots of dissolved gas, so it tends to erupt explosively, intermediate to felsic

ash

a pyroclastic that is less than 2mm in diameter, very powdery and remains suspended in the air for a long time, created during explosive eruptions

basaltic magma

has a lower viscosity and less dissolved gas trapped in it, so it tends to erupt gently, mafic magma

batholith

LARGE magma chamber that solidifies underground, has an exposed surface area greater than 100 km2

caldera

Large depressions are caused by the collapse of the ground above an emptied magma chamber, found at continental hotspots

cinder cone volcano

The “ant hills” of the volcano world - can pop up in any plate tectonic setting, steep slopes and an abnormally large crater

clinkers

composed of broken lava blocks, part of a’a lava, makes a clinking sound

coarse-grain

with large crystals, between fine and very course, also called phaneritic; granite, diorite, gabbro

concordant

forms parallel to surround rock (country rock), many types

crystallization

the process of forming crystals; the longer it takes to cool, the larger the crystals will be

dike

discordant; leads to two types of volcanic features, volcanic pipe and volcanic neck

create mini lines like scars leading to volcanic features

discordant

cuts across layers of surrounding rock (country rock), usually vertical-ish

extrusive (volcanic)

surface, forms on the exterior of the planet, forms from volcanoes

felsic

high silica, light color, low Mg and Fe levels

• magma that is more ----- it will have a higher viscosity, larger amount of gas trapped, and more explosive

fine-grained

smallest crystals, without being coarse, also called aphanitic; rhyolite, basalt, andesite

glassy

this texture is formed when lava forms very quickly above the surface, obsidian has this

hornito

a small spatter cone that forms on the surface of a lava flow (usually pahoehoe), typically steep sided and form standalone pinnacles or stacks.

igneous rock

FIRE = formed from magma or lava

intermediate

between felsic and mafic; in between silica, color, and Fe and Mg composition

intrusive (plutonic)

under the surface, interior of the Earth, forms from plutons

kipuka

a small piece of land completely surrounded by lava flows, like an island in lava, a piece of land lava misses

laccolith

forms when magma is injected between two layers of sedimentary rock underground, the pressure of the magma intruding between preexisting layers causes the overlying rocks to dome up, creating a mushroom shape

lahar

rapidly flowing mixture of rock debris and water that originates on the slopes of a volcano, also referred to as volcanic mudflows/debris flows.

What it takes to create it:

• loose volcanic debris (ash, lapilli etc.)

• water (often rains after eruption due to water vapor and condensation nuclei added to air also melting from snowcap)

• steep slope (Composite Cones are steep)

lapilli

Latin for “little stone,” and is a pyroclastic that is between 2mm and 64mm (a tennis ball) in diameter, least deadly pyroclastic

lava

hot, molten or semi-molten rock that has reached the surface

Only liquid and solid

• Most dissolved gases have escaped

lava bench

is a platform formed by new lava flows that extends the old shoreline, making new land, highly unstable because they often are underlain only by loose material such as sand and wave-eroded rock.

lava block

is a pyroclastic larger than 64 mm, comes from parts of volcanic cone getting blasted in air

lava bomb

is a large pyroclastic that is still molten as it flies, Bombs often have a streamlined shape (like Pele’s tears)

lava lake

large volumes of molten lava, usually basaltic, contained in a volcanic vent, crater, or broad depression

• Mt. Nyiragongo is the largest ------ in the world

tree molds

are cylindrical hollows left behind in a lava flow if the lava has completely incinerated the tree it once flowed around

lava tree

are formations created when pahoehoe flows around a tree and cools to form a crust around the trunk.

lava tube

is a natural conduit through which lava travels beneath the surface of a lava flow. Tubes form by the crusting over of lava channels and pahoehoe flows.

mafic

low silica content but high magnesium and iron content (“mafic” stands for “magnesium” and “iron”), generally darker in color

magma

hot, molten or semi-molten rock located under ground

------is made up of solid, liquid, and gas:

• the liquid portion is referred to as the melt

• the solid portion is made of minerals that crystallize directly from the melt; known as the mush

• solid rocks picked up on the way out called xenoliths or inclusions

• the gaseous portion is dissolved into the magmaocation beneath the vent of a volcano where molten rock (magma) is stored prior to eruption

magma chamber

la partially or totally molten body located in the earth's crust and capable of supplying magma to volcanic eruptions, location beneath the vent of a volcano where molten rock (magma) is stored prior to the eruption

pahoehoe

lava that has a smooth (yet often wrinkled) surface.

Many appearances:

• toe

• ropy

• coil

• entrail

Pele

the Hawaiian goddess of vocanoes

Pele’s Hair

is a naturally-spun volcanic glass that is blown away from lava fountains, cascading lava falls, or turbulent lava flows, gold in color and very fine (diameter of less than half a millimeter)

Pele’s Tears

small bits of molten lava in fountains can cool quickly and solidify into glass particles shaped like spheres or tear drops

pillow basalt

a volcanic igneous rock that forms when lava of basaltic composition comes from an underwater volcano

pluton

igneous rock formations that cool and solidify below the surface

1. magma is molten underground

2. formed after the magma has cooled underground

3. erosion exposes them at the surface

pyroclastics (tephra)

fragments of volcanic rock and lava blasted into the air by a volcanic eruption

• Classified by size

  • Ash-->lapilli-->blocks & bombs

• more deaths than lava & poison gas

pyroclastic flow

is a ground-hugging avalanche of hot ash, rock fragments, and volcanic gas that rushes down the side of a volcano at 100 - 400 mph or more!!

• the temperature within may be greater than 500° C.

• The deadliest hazard in a volcanic eruption

rhyolitic magma

Magmas here are felsic (remember that means highest in silica content), the fancy name

Rift Eruption (Curtain of Fire)

part of divergent volcanism, on land, a wall of lava fountains erupted from a crack

Ring of Fire

refers to region surrounding the Pacific plate where an increased amount of volcanism takes place due to subduction, lots of stratovolcanoes

shield volcano

Volcanoes made at oceanic hotspots; very tall and very wide, made mostly of lava flows piling up over and over, eruptions here will generally be mild due to less silica and lower viscosity (mafic and basaltic magmas)

silica

oxygen and silicon, the more ---- the thicker and more viscous it is, higher presents in felsic rocks/lava

sill

Pluton that is concordant (Parallel to bedding structures), surrounded by country rock (rock that was originally layered)

• Ex: Palisades of NY & NJ on Hudson River

skylight

an opening in the roof of a lava tube

stock

smaller version of a batholith, has an exposed surface area less than 100 km2

stratovolcano (composite volcano)

formed at convergent subduction volcanism

• are the “classic volcano shape”

  • Taller than wide, made of alternating layers of lava and pyroclastics

• lots around Ring of Fire

texture

is affected by cooling rate; larger crystals the longer it takes to cool

three main -----:

• glassy

• vesicular (gassy and full of air holes)

• fine-grained/aphanitic

• coarse-grain/phaneritic

• very coarse-grain/pegmatitic

tsunami

can be generated when a volcanic eruption abruptly displaces ocean water by either an explosion or landslide, a Japanese word with the English translation, "harbor wave”,

very-coarse grained (pegmatitic)

with largest crystals, took longer to cool; pegmatite

vesicular

gassy and full of air hole, no crystals; pumice, scoria, vesicular basalt

viscosity

measures a liquid’s resistance to flow

• Thicker = High Viscosity

• “High viscosity” flows slowly

• “Low viscosity” flows fast

• The more silica a magma has in it, the thicker and more viscous it is

Volcanic Explosively Index (VEI)

measures the amount of ash and debris thrown into the atmosphere during eruptions, eruptions with a large --- can significantly alter the climate for years

• scale from 1 (less ash and debris, 0.0001 km) - 10 (most ash and debris, 1,000 km)

volcanic fissure

a crack in the ground that allows lava to shoot into the air

volcanic neck

vertical structure left exposed once the outside of the volcano weathers and erodes away, discordant

*the volcano around it has been eroded away

volcanic pipe

solid lava conduit from magma chamber to surface, discordant

*there is a volcano surrounding it

Mined for diamonds in northern Canada!

xenolith (inclusion)

solid rocks picked up by magma, a piece of rock within an igneous rock that is not derived from the original magma but has been introduced from elsewhere, especially the surrounding country rock

volcanism

refers to the activity of magma forming and coming toward surface

volcano

the landform created when magma reaches the surface through an opening in Earth’s crust

country rock

rock that was originally layered

volcano

is the landform created when magma reaches the surface through an opening in Earth’s crust

volcanism

refers to the activity of magma forming and coming toward surface