Magma vs. lava and rocks
What is an igneous rock?
A rock formed when molten rock (magma or lava) cools and solidifies.
How can you tell intrusive vs extrusive rocks apart in the field?
Large crystals → intrusive
Small/no crystals or vesicles → extrusive
What three factors control magma cooling time?
Size of magma body
Depth underground
Temperature difference with surrounding rock
describe Cinder cone
a small, steep volcano made mostly of volcanic ash, cinders, and rock fragments.
What style of volcano forms at convergent boundaries (continental arcs)?
Large stratovolcanoes with explosive eruptions, often producing ash and pyroclastic flows.
What is the difference between magma and lava?
Magma is molten rock beneath Earth’s surface. Lava is magma that has erupted onto the surface.
Where do intrusive vs extrusive rocks form?
Intrusive → underground magma chambers
Extrusive → volcanoes, lava flows, mid-ocean ridges
Describe: magma chamber
an underground reservoir where magma collects beneath a volcano.
describe Stratovolcano
a tall volcano built from layers of lava and volcanic debris, often with explosive eruptions.
What style of volcanism forms at continental rifts?
Basaltic eruptions from fissures as continents begin to split apart.
What is an intrusive igneous rock?
Forms below Earth’s surface, cools slowly, and has large visible crystals (coarse-grained).
What are the three causes of melting?
Decompression melting (pressure drops)
Flux melting (water added)
Heat transfer melting (hot magma heats surrounding rock)
describe fissure
a long crack in Earth’s crust where lava can erupt.
describe Shield volcano
a broad volcano with gentle slopes formed by very fluid lava flows.
What style of volcano forms at oceanic hot spots?
Shield volcanoes made from fluid basaltic lava (often forming island chains).
What is an extrusive igneous rock?
Forms at Earth’s surface, cools quickly, and has small or no crystals (fine-grained or glassy).
What factors control the type of magma produced?
Temperature, pressure, water content, and composition of the source rock
describe crater
a bowl-shaped depression at the top of a volcano around the main vent.v
What style of volcano forms at mid-ocean ridges?
Basaltic lava erupts along long fissures, forming new ocean crust with mostly gentle eruptions.
What style of volcanism forms at continental hot spots?
Explosive eruptions that can form large calderas.
What is an extrusive igneous rock?
Forms at Earth’s surface, cools quickly, and has small or no crystals (fine-grained or glassy).
Why does magma rise?
Magma is less dense than surrounding rock, so it rises due to buoyancy.
describe caldera
a large depression formed when a volcano collapses after a major eruption empties the magma chamber.
What style of volcano forms at convergent boundaries (island arcs)?
Stratovolcanoes with explosive eruptions caused by gas-rich magma from subduction.
What are flood basalts?
Massive eruptions where huge amounts of lava flow from fissures and cover large regions.