Magma liquid molten rock underground Lava magma that

Magma: liquid, molten rock underground Lava: magma that reaches the surface

The composition of lava depends on dissolved gases and silica content

Dissolved Gases Example: water vapor, carbon dioxide (CO 2), sulfur (S) *More gas = more explosive eruption

Silica Content More silica (Si. O 2) = thick magma Viscosity- ability to resist flow. High viscosity = thick flow Low viscosity = thin flow

Two classifications of lava: 1) Felsic: much silica, lightcolored, slow moving (continental crust)

2) Mafic: low silica and gas, dark-colored, fast moving (oceanic crust)

3 types of mafic lava: 1) Aa Lava= choppy 2) Pahoehoe = ropy

3) Pillow Lava= underwater

Hardened Lava In Hawaii

Volcano: place where magma reaches the surface Volcanism: when a fissure or crack develops in the crust allowing magma to reach the surface

Pahoehoe

HOT SPOTS: areas of volcanic activity in the middle of lithospheric plates

Hawaiian Islands

• Volcano Anatomy 1. Vent: opening from which lava flows 2. Crater: funnel-shaped pit or depression at top of volcano 3. Caldera: depression where the walls have collapsed

Volcanic vents turn into plugs when the lava cools

Diamond Head Crater in Hawaii

Pyroclastic Material (tephra): solid particles produced in eruptions 1. Ash (<2 mm) 2. Lapilli (<64 mm) 3. Bombs 4. Blocks

ash

lapilli

bombs

blocks

Types of volcanoes…

• composed of calm lava flows • form gently sloping, domeshaped mountain • basaltic (mafic) magma

Example: largest = Mauna Loa in Hawaii

• Made mostly of tephra and other rock particles • Formed from explosive eruptions • small, narrow base & steep sides • Grantic (felsic) magma

• Symmetrical build up of alternating layers of rock and lava • highly explosive eruptions with high silica and high gas content • forms large, cone-shaped mountains

Composite example 1 Mt. St. Helens- before

Mt. St. Helens- after

Ex. 2 -Mount Vesuvius - Pompeii 20 feet of volcanic ash smothered The city!

Mount Vesuvius – Pompeii= composite 20 feet of volcanic ash smothered The city!