Volcanoes (part 2) Earth Science - 6 th Grade; Week 16; Mrs. Rubright

Review of Volcano Formation Heat and pressure cause rocks to melt and form magma. Magma needs to get out, too much pressure!!!!!! Rise in temperature or drop in pressure causes magma to form faster.

Where do most volcanoes occur? Volcanoes occur at both divergent and convergent boundaries and also at hot spots.

Why do we have different types of Volcanoes? The process of magma formation is different at each type of plate boundary. Therefore, the composition of magma differs in each tectonic setting. Tectonic settings determine the types of volcanoes that form and the types of eruptions that take place.

Types of volcanoes

Shield volcano: usually form at hot spots, from non explosive eruptions Cinder cone volcano: a small, cone-shaped volcano built of ash and cinders; form from explosive eruptions, very steep. Composite volcano: a deep-sided volcano of lava, ash, and cinders; form from both explosive and non explosive eruptions.

Shield volcano Form from many layers of “runny” lava. Very wide, not to steep. Biggest type of volcanoes Tallest mountain in the world is Mauna Kea (measures from sea floor to top) non explosive eruptions

Mauna Kea, Hawaii

Cinder cone volcano Smallest type of volcano Most common Made from pyroclastic material (material shot out of a volcano) Form a large crater Explosive!

Paricutin, Mexico

Composite volcano: Eruptions alternate between explosive and non-explosive. Sometimes they have runny lava layers, other times the have pyroclastic materials form layers. Have a wide base and steep sides. Have a crater Mount Fuji

2 Types of eruptions Explosive: volcanoes that build enough pressure to blow its top, sending pyroclastic material into the air. Non explosive: Build only enough pressure to allow lava to run down its sides. Eruption Recipe Thin magma, little gas → quiet eruption Thin magma, much gas → big eruption Thick magma, little gas → quiet eruption Thick magma, much gas → BOOM!

Non explosive eruption Mafic: refers to rocks and magma rich in iron and magnesium. This type of lava that is very runny. As magma nears the surface there is little pressure, causing gasses escape easily. Magma low in Silica have quiet eruptions

Explosive eruptions Felsic: means magma with high silica and feldspar content. Felsic magma traps water and gas bubbles, which leads to lots of pressure. Silica acts like a cork Explosive eruptions are caused by a build up of high pressure. Convergent zones contain lots of water, therefore have explosive eruptions.

Pyroclastic materials Material that is thrown into the air during an explosion. Volcanic bombs: large blobs of magma that harden in the air. Lapilli: pebble size rocks Volcanic ash: tiny powder like material

Pyroclastic materials Solid volcanic material such as ash and rocks that is thrown into the air during an explosion. Volcanic bombs: large blobs of magma that are shot into the air; harden in the air. Lapilli: pebble size rocks Volcanic ash: tiny powder like material

Four types of lava Aa: lava that has a rough surface Pahoehoe: lava that has a smooth or billowy surface; forms thin crust and wrinkles Pillow lava: lava that erupts under water, has a round shape Blocky lava: cooler, lava that does not travel far from eruption, jagged when it dries.

Aa lava that is thick and sharp

Pahoehoe: forms thin crust and wrinkles

Pillow lava lava that erupts under water, has a round shape

Stages of a Volcano There are 3 stages to a volcano's life –Active: a volcano that has erupted recently or will erupt soon –Dormant: a volcano that has not erupted for a long time by may erupt again –Extinct: a volcano that can no longer erupt

Questions What is the difference between magma and lava? What do you think determines how easily lava flows? Relate the shapes of volcanoes to their explosivity. Why do you think that many people believe all volcanoes are dangerous and explosive?