gel 1 - week 5

what are Intrusive igneous rocks?

crystallize below ground

what are extrusive igneous rocks?

crystallize on Earth’s surface

what is magma?

a mixture of melt and crystals

what is lava?

refers to magma that reaches the surface

what are the three ways to melt a rock?

• Decrease pressure

• Increase temperature

• Add volatiles

how are igneous rocks classified?

on the basis of silica (SiO2) content (Mafic versus intermediate versus felsic

what are processes that affect magma (or melt) composition?

• Partial melting of parent rock

• Assimilation of country rock

• Magma mixing

• Fractional crystallization

how do minerals crystallize?

at predictable temperatures and in a predictable sequence during magma cooling

what does fractional crystallization lead to?

a diversity of rock compositions

what does mafic magmas crystallize?

olivine, pyroxene, and Ca-rich plagioclase

what does felsic magma crystallize?

quartz, K-spar, Na-rich plagioclase, biotite, and amphibole

what do crystal zonations do?

record changes in magmatic conditions

cooling vs crystals

• faster cooling = smaller crystals

• slower cooling = larger crystals

what does magma viscosity depend on?

temperature, composition, and water content

what are sills?

horizontal, sheet-like intrusions between rock layers

what are dikes?

vertical or cross-cutting wall-like intrusions

what are cylindrical pipes?

vertical conduits that bring magma to the surface

what do magma pathways lead to?

sills, dikes, and cylindrical pipes

plutons vs. batholiths

plutons are medium-sized intrusive bodies; batholiths are massive features composed of many individual plutons.

what is the igneous classification?

crystalline (coarse vs. fine) vs. fragmental vs. glassy

what are magma chambers?

Underground reservoir of molten rock

what are vents/fissures?

Openings (circular or linear) where eruption occurs

craters vs. calderas

Craters are small bowl-shaped depressions; Calderas are giant depressions formed by the collapse of a volcano

what are the types of volcanoes?

shield volcanoes, cinder cones, stratovolcanoes

what are shield volcanoes?

broad/low profile

what are cinder cones?

small, steep piles of tephra

what are stratovolcanoes?

large, classic cone-shaped

what are explosions favored by?

• High SiO2

• High gas pressure

• High viscosity

what is volcanic behavior?

complicated and difficult to predict because these factors can vary in space and time

size of eruptions vs frequency

Large volcanic eruptions are less frequent

what is the “magnitude scale” for volcanic eruptions?

the VEI (Volcano Explosivity Index)

what does the VEI depend on?

• Plume height

• Volume of magma

what do flood basalts represent?

• the eruption of the head of a mantle plume

what do hot spot tracks represent?

the eruption of the tail of a mantle plume

what can flood basalt cause?

mass extinctions

Volcanoes are hazardous due to?

• Lava flows and pyroclastic flows

• Ash fall (aviation)

• Landslides

• Lahars

• Earthquakes & tsunamis

• Dangerous gasses

what do volcanoes do?

often provide warning of an imminent eruption

volcanic monitoring

There are numerous tools for monitoring activity

Based on the diagram below, which rock is more dense: granite or peridotite? 

peridotite

Based on the diagram below, which of the following rocks contains the most FeO? 

rhyolite, andesite, basalt

basalt

Based on the diagram below, what minerals would you find in a granite or rhyolite? (select all that apply) 

olivine

amphibole

pyroxene

plagioclase

K-feldspar

biotite

quartz

 

amphibole

plagioclase 

K-feldspar

biotite

quartz

In comparison to mafic rocks, silicic (or felsic) rocks tend ________.

to be less dense and erupt at lower temperatures

to be more dense and erupt at higher temperatures

to be less dense and have lower silica content

to be less dense and have lower viscosity

to be less dense and erupt at lower temperatures

The three ways to melt a rock are _________

increase temperature, decrease pressure, increase volatile contents

increase temperature, increase pressure, increase volatile contents

increase temperature, increase pressure, decrease volatile contents

increase temperature, decrease pressure, decrease volatile contents

increase temperature, decrease pressure, increase volatile contents

Intrusive igneous rocks that form by slow cooling of magma in the subsurface tend to have ________ than extrusive igneous rocks

more glass

larger crystals

smaller crystals

faster cooling rates

larger crystals

Andesite and rhyolite lavas are ______ viscous and are generally _______ in gas than basalt lavas. These properties tend to make rhyolite eruptions more explosive than basalt eruptions. 

more / richer

more / poorer

less / richer

less / poorer

more / richer

Match the letter with the volcanic feature.  Not all words will be used. 

options: crater, pre-volcanic basement, vent, lava flows, dike, tephra, sill, alluvium, magma chamber

a. crater

b. vent

c. dike

d. sill

e. magma chamber

Examine the hazard map below.  Approximately how far from the summit of Mount Rainier does the "area most likely to be affected by lava flows and pyroclastic flows" extend? 

less than 1 kilometer

several kilometers

several tens of kilometers

several hundreds of kilometers

several kilometers