Volcanoes

Shield Volcanoes Basaltic magma - from oceanic crust – very dense Shield shaped- more flat and rounded than other volcanoes – wider than tall Very quiet non-explosive eruption - Lava erupts from the rift zones or faults on the surface of the cone

KILAUEA Exists as a shield volcano One of the most active volcanoes on Earth Towers at a height of 4,190 feet above sea level 1,000 year old lava envelopes the exterior of this volcano KILAUEA January 3,2003 – 20 year old birthday of eruption that is still going on – Longest eruption known in Earth’s existence

Hot Spots Hot Spots: Not all volcanoes develop along plate boundaries. Sometimes magma works its way up through earth’s lithospheric plates. Areas where this occurs is called a hot spot. Hot spots appear to be stationary but are they really? ______ Why? ______________________________________________________________________________________________________. What is an example of a hot spot? __________________________

Volcanic Hot Spot Audio and Visual click here to view and listen to how hot spots are created

Cinder Cone Volcano Characteristics Granitic lava- only continental crust “Narrow” bases and the steepest sides Pyroclastic (aka - tephra) explosions - mixtures of hot, dry rock fragments and hot gases – VERY EXPLOSIVE

Paricutin Now stands at a height of 10,400 ft. (3170 meters) Only one eruption in history—lasted from 1943 to 1952 Inactive since then Once cinders erupted, the cone was slowly built up and added to over the years in size A cinder cone volcano Located in Mexico February 20, 1943—Farmer noticed bulge growing in cornfield-within week grew to 100 meters in height Within five months of the first eruption, the town was evacuated and lay covered in ash and lava

Composite Volcanoes Made of granitic and basaltic lava Tall and Wide Mountains - “Middle sized volcano” Tephra (pyroclastic) and lava flows (at different times)…Can be quiet or very explosive Examples: Mount Rainier, Mount St. Helens, Mount Shasta, Mount Hood

Mount St. Helens Example of a composite volcano Located in the state of Washington, USA First estimated eruption occurred about 10,000 years ago Summit stands at 8,363 feet 57 people died in the 1980 eruption Also the most examined eruption in recent history Most recent eruption was in 1990 Oldest rocks on mountain = 40,000-50,000 years old 1980 eruption is one of the most powerful eruptions by Mt. St. Helens in its history