hazardous earth - tectonic hazards (flashcards)

eq3 : why do the causes and impacts of tectonic activity and management of tectonic hazards vary with location?

facts about the earth’s crust

• thinnest layer

• made of rocks (solid)

• divided in 15 tectonic plates

• consists of oceanic and continental crust

facts about the earth’s mantle

• semi-solid material

• thickest layer

• upper and lower mantle - upper is mostly solid but some melting at plate boundaries

• becomes hotter and denser with depth

what is the outer core made of?

• made of molten layer of iron and nickel

facts about the earth’s inner core

• made of iron and nickel

• densest layer

• solid ball

• composed mostly of iron

• pressure is so high, it never melts

what is oceanic crust?

part of earth’s crust which is:

• underwater

• thinner (than continental)

• made of basalt

• denser/heavier (than continental)

• newer (than continental)

what is continental crust?

part of the earth’s crust which is:

• thicker (than oceanic)

• made of granite

• less dense/lighter (than oceanic)

• older (than oceanic)

what is the lithosphere?

rigid layer, lower part of the earth’s crust and lies on top of the asthenosphere.

what is the asthenosphere?

upper part of the mantle. high temperature and pressure is low enough so rocks can flow very slowly.

what is a plate boundary/margin?

this is where two plates meet.

tectonic activity such as volcanoes and earthquakes are common along a plate margin.

types of plate boundary

• constructive/divergent

• destructive/convergent

• transform/conservative

• collision

convection currents

convection currents move circular in motion

in the lower mantle, the rock is heated by the core and rises slowly towards the crust and begins to cool.

at the asphenosphere, the rock is forced to move sideways.

as it cools, it sinks slowly to the core, then forced sideways, and is heated by the core until it rises again.

convection currents drag the plates above to move them apart.

how do constructive/divergent boundaries work?

• convection currents pull apart the two plates and widen the gap between them

• rising heat and reduction in pressure causes the asthenosphere to melt, forming magma

• magma rises to fill the gap, which will eventually solidify, forming new land/volcanoes

• e.g. Mid Atlantic Ridge - Eurasian plate moves away from North American plate

how do destructive/convergent boundaries work?

• convection currents cause plates to move towards each other

• when oceanic plate meets continental plate, the denser oceanic plate sinks under the less dense continental plate - this is subduction

• as oceanic plate subducts, magma rises and may eventually break through earth’s surface, forming composite volcano

• e.g. Andes Mountains - Nazca and South American plates move towards each other

how do conservative boundaries work?

• as plates slide past, they sometimes cause friction and build up pressure →when they get past, the pressure is released, shock waves are sent to the surface

• plates can move in opposite directions and similar direction, but different speeds

• as crust is neither created or destroyed, there are no volcanoes but the friction causes earthquakes

what are volcanoes?

openings in the earth’s crust, or vents where lava, tephra (small rocks) and steam erupt onto the earth’s surface.

shield vs composite volcanoes

shield:

• non-violent

• gentle slope

• wide base

• lava is fluid

composite:

• violent

• steep slope

• high with narrow base

• acid lava and ash

describe the two types of lava

basic lava:

• low silica content

• takes longer to cool so flows over long distances

• less viscous (less thick)

acid lava:

• high silica content

• travels only short distances

• higher viscosity

what is an earthquake?

sudden and short period of intense ground shaking caused by a release of seismic energy

what is the focus of an earthquake?

where an earthquake originates deep within the earth’s crust

what is the epicentre of an earthquake?

the place on the surface of the earth directly above the focus