geo simplifyied

Igneous Rocks form when

magma or lava crystallizes (solidifies)

Intrusive (Plutonic)

Magma cools underground → large crystals (ex: granite, gabbro).

Extrusive (Volcanic)

Lava or pyroclastics cool at surface → fine-grained/glassy (ex: basalt, obsidian).

convergent

subduction zones

divergent 

mid-ocean ridges

Magma

Molten rock underground.

Lava

Magma that erupts at the surface.

Pyroclastics

Fragments blown out (ash, lapilli, bombs, blocks

Mafic lavas

runny, quiet eruptions.

Felsic lavas

sticky, explosive eruptions.

magma temp

700-1200 * C

geothermal gradient

25 degrees celcius per kilo

Magma crust made of

silica-rich

Magma mantle made of

Fe-Mg silicates

Magma Depth of origin

~100–300 km

magma path

melt rises → collects in magma chamber → solidifies as pluton or erupts as lava/pyroclastics.

Bowen’s Reaction Series

Predicts mineral crystallization order as magma cools.

Discontinuous branch (ferromagnesians)

Olivine → Pyroxene → Amphibole → Biotite.

Continuous branch (feldspars):

• Ca-rich plagioclase → Na-rich plagioclase.

last to form

Orthoclase, Muscovite, Quartz.

Bowen’s reaction series explains why

felsic magma evolves from mafic magma (crystal settling).

Magma Origins

Spreading ridge, Subduction zones, Hot spots

Spreading ridge

divergent

Spreading ridge definition

decompression melting → mafic magma (basalt).

Subduction zones

convergent

Subduction zones definition

water lowers melting temp → intermediate/felsic magmas (andesite, rhyolite).

Hot spots

mantle plumes create volcanism inside plates (Hawaii, Yellowstone).

Assimilation

absorbs country rock.

Aphanitic

fine-grained, extrusive, rapid cooling. basalt

Phaneritic

coarse-grained, intrusive, slow cooling. granite

Porphyritic

mixed crystal sizes, complex cooling.two cooling rates = big + small crystals.

Glassy

no crystals (obsidian) cooled instantly

Vesicular

contains gas bubbles, gas bubbles trapped (pumice, scoria).

Pyroclastic

made of volcanic fragments, welded together (tuff, breccia).

Mafic

Dark, Ca-plagioclase + pyroxene (basalt, gabbro).

felsic

Light minerals, quartz, feldspar (granite, rhyolite).

Concordant

parallel to country rock: Sill, Laccolith.

Discordant

(cuts across rock): Dike, Batholith, Stock, Volcanic neck.

Batholiths

giant body >100 km² (Sierra Nevada).

Cooling rate

texture

Silica content =

viscosity + eruption style

Magma origins depend on

tectonic setting.

Bowen’s Series explains

mineral order.

Plutons are intrusive bodies classified by

shape/size.

volcano

is basically a “plumbing system” where magma, gases, and pyroclastics escape to the surface through a vent.

Volcanism

all processes that bring magma/gas to the surface.

active volcano

erupting or likely to erupt.

Dormant volcano

“asleep,” hasn’t erupted recently but could

extinct volcano

unlikely to erupt again

Eruption Components

Volcanic gases, Lava flow, and Pyroclastic materials

Volcanic gases

mostly water vapor, carbon dioxide, sulfur dioxide.

• Gases drive eruptions (like shaking a soda bottle).

Lava flow

molten rock at the surface.

Pyroclastic materials

fragmented material blasted out: ash, lapilli, bombs, and blocks

Pahoehoe

smooth, ropy, fast-flowing basaltic lava.

Aa

rough, jagged, blocky.

Pillow lava

• forms underwater, looks like blobs/pillows

Columnar joints

hexagonal cracks that form as lava cools & contracts

ash

(<2 mm): fine, can travel long distances by wind.

Ash fall

settles from air

Ash flow

hot, fast-moving cloud hugging the ground → pyroclastic flow.

Lapilli (2–64 mm)

pebble-sized, build up around vent → cinder cones

Bombs (>64 mm)

ejected molten, aerodynamic shapes (like footballs).

Blocks (>64 mm)

solid rock chunks, angular, often pieces of volcano walls.

Craters

small depressions >1 km

Calderas

huge collapse structures after massive eruptions

Basalt plateaus

vast, flat from fissure eruptions

pyroclastic sheets

widespread ash deposits, often linked to calderas

Shield volcanoes

• Broad, gentle slopes.

• Basaltic, runny lava.

• Quiet eruptions (Hawaii)

Cinder cones

• Small, steep-sided.

• Made of pyroclastics (lapilli, ash).

• Erupt once or briefly, then extinct.

Composite/Stratovolcanoes:

• Large, steep, layered with lava & pyroclastics.

• Explosive, dangerous.

• Found at convergent boundaries (Mt. St. Helens, Mt. Fuji, Andes).

Lava domes

• Small, steep, very viscous felsic magma.

• Grow slowly, collapse explosively.

Ring of Fire (Pacific belt)

~60% of all volcanoes (e.g., Cascades, Andes, Japan).

Mediterranean belt

~20% (Etna, Vesuvius, Santorini).

Intraplate hotspots

away from boundaries (Hawaii, Yellowstone).

Divergent boundaries

basaltic magma erupts at ridges/fissures (Iceland, East African Rift).

Convergent boundaries

subduction → felsic/intermediate, explosive stratovolcanoes (Cascades, Andes).

Intraplate hotspots

mantle plumes punch through plates (Hawaii, Yellowstone).

VEI (Volcanic Explosivity Index)

scale 0–8, measures eruption size.

Pyroclastic flows

most deadly → fast, hot clouds of gas + ash.

Lahars

volcanic mudflows, triggered when ash mixes with water.

Weathering

The breakdown of rocks into smaller pieces.

two types of weathering

Mechanical (physical) & Chemical

mechanical (physical) weathering

breaks into pieces, no change in composition

Chemical weathering

Alters the minerals; composition changes

Erosion

Movement of weathered material by water, wind, glaciers, or currents

soil

A mix of weathered rock + organic matter + water + air that can support plants.

Parent Material

The original rock or sediment that soil develops from.

Sedimentary rocks

only ~5% of crust, but cover ⅔ of surface — because weathering & erosion pile them up everywhere.

Mechanical Weathering

rocks break apart but stay the same mineral.

Frost wedging (freeze-thaw)

• Water freezes → expands 9% → cracks rocks.

• Creates talus (rock piles at base of slopes).

• Common in mountains.

Pressure release (exfoliation):

• Rocks formed under pressure expand near the surface.

• Forms sheet joints & exfoliation domes.

• Think: “peeling layers off an onion.”

Thermal expansion

• Repeated heating/cooling → cracks.

• Common in deserts with hot days/cold nights

Salt crystal growth

• Saltwater evaporates, salt crystals grow → push rock apart.

• Common in deserts & coastlines

Biological activity:

• Roots pry rocks apart.

• Burrowing animals loosen soil.

Chemical Weathering

minerals react with water, air, acids → become new minerals.

chemical weathering examples

solution: oxidation, hydrolosis

soil

= regolith + air + water + organic matter.

Regolith

weathered rock that covers land.

Residual soil

forms in place

Transported soil

formed elsewhere, moved by water/wind/glacier.