Study GuideTest2 - GEOL Study Guide Test 2 Chapter 6...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
GEOL Study Guide: Test 2 Chapter 6: Volcanoes The diagnostic characteristics of a volcano A volcano is a vent where magma and other volcanic products erupt onto the surface Most volcanoes have a crater , a roughly circular depression usually located near the top of the volcano. Volcanoes consist of volcanic rocks , which form from lava, pumice, volcanic ash, and other products of volcanism. Besides erupting from volcanoes that have the classic shape of a cone, magma erupts from fairly linear cracks called fissures , and from huge circular depressions called calderas . Why is every hill composed of volcanic rock not a volcano? Flat topped hills called mesa’s consisting of volcanic rock are not volcanoes because they did not form over a volcanic vent, instead, it is an eroded remnant of a once extensive lava flow. The four main types of volcanoes Scoria Cones are cone-shaped hills several hundred meters high, usually with a small crater at their summit. Some scoria cones form next to or on the flanks of composite and shield volcanoes. Shield volcanoes have broad, gently curving slopes and can be relatively small (less than a kilometer across) or can form huge mountains tens of kilometers across and thousands of meters high. They commonly contain a crater or line of craters and fissures at their summit. Composite volcanoes are typically fairly symmetrical mountains thousands of meters high with moderately steep slopes and a crater at the summit. They may be large but on average are smaller than shield volcanoes. Volcanic domes are dome-shaped features that may be hundreds of meters high. Domes include some volcanic ash intermixed with rock fragments derived from solidified lava in the dome. Many domes are within craters of composite volcanoes. The relative sizes of different types of volcanoes Composite Volcano Small Dome Shield Large Shield Scoria Cone Four ways magma erupts
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Lava Flow – When magma erupts onto the surface and flows away from a vent. Lava Dome – Forms from the eruption of highly viscous lava, this causes the lava to pile up around the vent instead of flowing away. Lava Fountain – Explosive eruptions that send molten lava into the air; these result from high initial gas content in less viscous lava. Tephra – Explosive eruptions that are a mixture of volcanic ash, pumice, and rock fragments ejected into the air. Difference between an eruption column and a pyroclastic flow, and the role that gas plays in eruptive style. Eruption Column – Tephra erupts high into the atmosphere forming an eruption column . The Tephra falls back to earth as solidified and cooled pieces of rock. An eruption column forms when large volumes of volcanic gas come out of the magma and overcome gravity to carry the cloud of Tephra into the atmosphere. Pyroclastic Flow
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 19

Study GuideTest2 - GEOL Study Guide Test 2 Chapter 6...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online