Chapter 10: Mountains and Volcanoes 10.1: Movement of rock builds mountains 10.2: Volcanoes form as molten rock erupts 10.3: Volcanoes affect Earth’s land, air, and water

Review Motion that transfers heat within a material Convection current The layer formed by Earth’s crust and the very top of the mantle Lithosphere Underwater mountain ranges found where the ocean floor is spreading Mid-ocean ridges

ç Alaska's Mount Redoubt volcano spews ash and steam during an eruption in Steam rises through the snow on Mount Redoubt in Alaska last year (2009) Iceland volcano, near the Eyjafjallajokull glacier, early Sunday, March 21, first major eruption there in nearly 200 years Iceland volcano, near the Eyjafjallajokull glacier, early Sunday, March 21, first major eruption there in nearly 200 years

Volcanoes erupt many types of material Volcano: opening in Earth’s crust through which molten rock, rock fragments, and gases erupt  A mountain built up from erupted material Recall: the surface is cool rock, but most of the Earth is extremely hot rock and molten metal  Some heat escapes to the surface through volcanoes Erupt violent (throw out rocks) or gently (rivers of molten lava  Depends on type of magma feeding the volcano

Magma Made of a large portion of silica (silicon and oxygen), gases High in silica: resists flowing, so expanding gases are trapped in it  Pressure builds up – the gases blast out in a violent dangerous explosion Poor in silica: flows easily, gas bubbles moves up through it and escape fairly gently  Can still throw lava high into the air – lava fountains – but it’s “safe” to be nearby Grinded silica _build.cfm?id=resour_ch3&u=3#%23

Magma Rises as long as it is less dense than the surrounding rock  When it stops rising, it collects in a “magma chamber” From here can cool (igneous rock) or erupt (lava)

Rock Fragments Form as:  Escaping gas bubbles pop, tearing magma apart  Larger pieces of lava are thrown into the air and cool  Rocks of all sizes are ripped from the volcano wall Ash: size of dust to rice grains  Can travel long distances, carried by winds Cinders: somewhat larger  Contains holes from escaping gases Bombs and Blocks: up to the size of houses!  Fall quickly

Volcanic Gases What looks like smoke is actually a mix of ash and gases Main gases: water vapor and carbon dioxide  Can combine with water in air to form acids Pyroclastic flow: a dense cloud of superhot gases and rock fragments that races downhill  As hot as 800C (1500F)!, travel faster than 160 km/hr (100 mi/hr)  Most dangerous type of volcanic eruption classzone volcanoes

Most volcanoes form along plate boundaries Common along tectonic plate boundaries where oceanic plates sink beneath other plates  Plates sinking deep into a subduction zone – heat and melt  magma  can build tall volcanic mountains Common where plates pull apart: allows magma to rise from the mantle  In the water, magma erupts at spreading centers and cools to form new lithosphere

Most volcanoes form along plate boundaries Less common: forming over a hotspot (far from a plate boundary) More than 400 volcanoes – 80% of all active volcanoes above sea level – are along subduction zones in the Pacific Ocean  Active = erupting or has erupted in recorded history  “Ring of Fire”

Volcanoes can have many shapes and sizes 1. Shield Volcano – shaped like a broad, flat dome Built up by many eruptions of lava that is relatively low in silica – flows easily and spread out in thin layers 2. Cinder Cone: steep, cone-shaped hill formed by the eruption of cinders and other rock fragments that pile up around a single crater Form as gas-rich magma erupts Escaping gases throw small chunks of lava into the air, where they harden before landing 3. Composite Volcano: a cone-shaped volcano built up of layers of lava and layers of rock fragments Magma high in silica, pasty Steep near the top and flattens out toward the bottom Have violent eruptions: Expanding gases trapped in rising magma tend to cause explosions Hardened lava from earlier eruptions often plugs openings in these volcanoes and is blow out of the way before any more magma can escape

aka composite

Crater Lakes Both shield volcanoes and composite volcanoes can form calderas – “huge crater formed by the collapse of a volcano when magma rapidly erupts underneath it”  Crater lakes: Oregon: formed 7700 years ago! Mount Mazama Volcano and Crater Lake Caldera, Oregon - Wizard Island

Scientists Monitor Volcanoes Before Mount Pinatubo (Philippines) erupted in 1991, it had not erupted in 500 years!  Erosion had changed its shape and so did not appear to be a composite volcano

Early indication that is was going to erupt - ash

Scientists Monitor Volcanoes Mount Pinatubo: scientists were able to warn locals and save many lives  Warning signs: many small earthquakes followed by explosions of steam near the top Indications that magma is moving below a volcano:  earthquake activity  changes in tilt of the ground  Temperature at openings, springs, and lakes  Amount and types of gases given off by the volcanoes  Increasing temperatures and gas changes indicate that fresh magma has moved in a shallow magma chamber Study age and types of volcanic rocks  Time passed between eruptions  How violent the eruptions were

Discovery.com Volcano Explorer ii/interactive/interactive.html ii/interactive/interactive.html