Geology Flashcards
Exam #2
Viscous
Explosive
Non-Viscous
Non-Explosive
Viscosity
A magma’s resistance to flow and depends on temp. and comp.
High SiO2 =
More Viscous(explosive) and magma solidifies at lower temps. making them even more viscous.
When magma rises to the earths surface it is called…?
Lava.
Mafic Magma silica content(%), viscosity, Eruption temps. (*C) and Eruption Style:
45-52% Silica
Low Viscosity
Up to 1300 *C
Flows
Intermediate Magma silica content(%), viscosity, Eruption temps. (*C) and Eruption Style:
53-65% Silica
Intermediate Viscosity
About 1000 *C
Flows and explosions.
Felsic Magma silica content(%), viscosity, Eruption temps. (*C) and Eruption Style:
> 65% Silica
High Viscosity
Less than 900 *C
Domes and explosions.
Shield Volcanoes
Are wide and gently sloping.
Fissures
A fissure vent, also known as a volcanic fissure or eruption fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is often a few metres wide and may be many kilometres long.
Flood basalt
A “flood basalt” is the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava
Lava Tubes
a natural tunnel within a solidified lava flow, formerly occupied by flowing molten lava.
Cinder Cones
A cinder cone or scoria cone is a steep conical hill of loose pyroclastic fragments, such as either volcanic clinkers, cinders, volcanic ash, or scoria that has been built around a volcanic vent.
Scoria
a cindery, vesicular basaltic lava, typically having a frothy texture.
Pyroclastic flow
A pyroclastic flow is a fast-moving current of hot gas and volcanic matter that moves away from a volcano about 100 km/h on average but is capable of reaching speeds up to 700 km/h.
Stratovolcanoes
A stratovolcano is a tall, conical volcano composed of one layer of hardened lava, tephra, and volcanic ash. These volcanoes are characterized by a steep profile and periodic, explosive eruptions. The lava that flows from them is highly viscous, and cools and hardens before spreading very far.
Tephra
rock fragments and particles ejected by a volcanic eruption.
Pumice
Glassy solidified magma that contains abundant gas bubbles
Ash
small crystals, rock fragments, and bits of glassy frozen magma
Dome
a lava dome or volcanic dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano.
Magma chamber
A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is under great pressure, and, given enough time, that pressure can gradually fracture the rock around it, creating a way for the magma to move upward.
Tuff
Volcanic ash that becomes lithified.
Lithification
the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. Essentially, lithification is a process of porosity destruction through compaction and cementation.
Caldera
A caldera is a large cauldron-like hollow that forms following the evacuation of a magma chamber/reservoir. When large volumes of magma are erupted over a short time, structural support for the crust above the magma chamber is lost.
Hotspot
A volcanic “hotspot” is an area in the mantle from which heat rises as a thermal plume from deep in the Earth. High heat and lower pressure at the base of the lithosphere (tectonic plate) facilitates melting of the rock. This melt, called magma, rises through cracks and erupts to form volcanoes.
Lahar
A lahar is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a river valley.
Aa flows
A’a is characterized by a rough, jagged, spinose, and generally clinkery surface. Aa lava flows tend to be relatively thick compared to pahoehoe flows. During the early episodes of the current eruption of Kilauea volcano, aa flows up to 36 feet (11 m) thick surged through the Royal Gardens subdivision at rates as great as 108 ft/min (33 m/min).
Pahoehoe
Pahoehoe is the second most abundant type of lava flow.
Pahoehoe lava is characterized by a smooth, billowy, or ropy surface.
Pahoehoe flows tend to be relatively thin, from a few inches to a few feet thick. In map-view the flows tend to be narrow and elongate.
Pillow lava
Pillow lavas are volumetrically the most abundant type because they are erupted at mid-ocean ridges and because they make up the submarine portion of seamounts and large intraplate volcanoes, like the Hawaii-Emperor seamount chain.
Eruptions under water or ice make pillow lava.
Alluvial Fan
a fan-shaped mass of alluvium deposited as the flow of a river decreases in velocity.
braided channel
A braided river, or braided channel, consists of a network of river channels separated by small, and often temporary, islands called braid bars or, in British usage, aits or eyots. Braided streams occur in rivers with low slope and/or large sediment load.
Cut Bank
Cut banks are found in abundance along mature or meandering streams, they are located on the outside of a stream bend, known as a meander, opposite the slip-off slope on the inside of the bend. They are shaped much like a small cliff, and are formed by the erosion of soil as the stream collides with the river bank.
Capacity
The capacity of a stream or river is the total amount of sediment a stream is able to transport. … Stream capacity is often mistaken for the stream competency, which is a measure of the maximum size of the particles that the stream can transport, or for the total load, which is the load that a stream carries.
Channel
a channel is a type of landform consisting of the outline of a path of relatively shallow and narrow body of fluid, most commonly the confine of a river, river delta or strait.
Delta
A delta is a fan of braided streams and sediment formed when a river discharges into a larger body of water: a sea or a lake. It will be useful if the reader has already read the article on rivers before reading further.
Discharge
In hydrology, discharge is the volumetric flow rate of water that is transported through a given cross-sectional area. It includes any suspended solids (e.g. sediment), dissolved chemicals (e.g. CaCO3(aq)), or biologic material (e.g. diatoms) in addition to the water itself.
Divide
Divide. A ridge or other topographic feature that separates two adjacent drainage basins. It is an imaginary line that separates two different directions of surface water flow.
flash flood
A flash flood is a rapid flooding of geomorphic low-lying areas: washes, rivers, dry lakes and basins. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, tropical storm, or meltwater from ice or snow flowing over ice sheets or snowfields. Flash floods may occur after the collapse of a natural ice or debris dam, or a human structure such as a man-made dam
Flood crest
it is the highest stage or level of a flood wave as it passes a particular point.
Flood frequency curve
A flood frequency curve is a valuable tool to extrapolate how often a flood of a given discharge will occur. A flood frequency curve can be constructed by plotting a graph of discharge versus recurrence interval.
Floodplain
Floodplain, also called Alluvial Plain, flat land area adjacent to a stream, composed of unconsolidated sedimentary deposits (alluvium) and subject to periodic inundation by the stream.