VOLCANIC LANDFORMS

These landforms are formed as a result of volcanic activity, or else they represent the various kinds of volcanoes and volcanic features themselves.

OVERVIEW…

CINDER CONES (TEPHRA CONES)

 Cinder cones are small volume cones consisting mainly of tephra that result from strombolian eruptions.  They usually consist of basaltic to andesitic material.Slopes of the cones are controlled by the angle of repose (angle of stable slope for loose unconsolidated material) and are usually between about 25 and 35o.

They show an internal layered structure due to varying intensities of the explosions that deposit different sizes of pyroclastics.

On young cones, a depression at the top of the cone, called a crater, is evident, and represents the area above the vent from which material was explosively ejected.

Cinder and tephra cones usually occur around summit vents and flank vents of stratovolcanoes.

Parícutin Volcano in Mexico. This volcano was born in a farmers corn field in 1943 and erupted for the next 9 years.Last eruption:1952

VOLCANIC DOMES (LAVA DOMES)

result from the extrusion of highly viscous, gas poor andesitic and rhyolitic lava.

Blocks of nearly solid lava break off the outer surface of the dome and roll down its flanks to form a breccia around the margins of domes.

Most dome eruptions are preceded by explosive eruptions of more gas rich magma, producing a tephra cone into which the dome is extruded.

They form unstable slopes that may collapse to expose gas-rich viscous magma to atmospheric pressure.  

This can result in lateral blasts or Pelean type pyroclastic flow (nuée ardentes) eruptions.

SHIELD VOLCANOESCharacterized by gentle upper slopes (about 5o) and somewhat steeper lower slopes (about   10o)

Most shields were formed by low viscosity basaltic magma that flows easily down slope away from the summit vent

Vents for most shield volcanoes are central vents, which are circular vents near the summit. 

Hawaiian shield volcanoes also have flank vents, which radiate from the summit and take the form of en-echelon fractures or fissures, called rift zones,  from which lava flows are released.

The term 'en echelon' refers to closely-spaced, parallel or sub-parallel, overlapping or step-like minor structural features in rock (faults, tension fractures), which lie oblique to the overall structural trend.

The three main volcanoes which make up the island of Hawaii:

Mauna LoaMauna KeaKilauea

Mauna Loa - largest landform on Earth

STRATOVOLCANOES(COMPOSITE VOLCANOES)

Have steeper slopes than shield volcanoes, with slopes of 6 to 10o low on the flanks to  30onear the top

Stratovolcanoes show inter-layering of lava flows and pyroclastic material, which is why they are sometimes called composite volcanoes.

sometimes have a crater at the summit that is formed by explosive ejection of material from a central vent

Mayon Volcano it holds the record of the world's most perfect volcanic cone.

MAARresult from phreatic or phreatomagmatic activity, wherein magma heats up groundwater, pressure builds as the water to turns to steam, and then the water and preexisting rock are blasted out of the ground to form a tephra cone with gentle slopes.

CRATERS AND CALDERAS Craters are circular depressions, usually less than 1

km in diameter, that form as a result of explosions that emit gases and tephra.

Calderas are much larger depressions, circular to elliptical in shape, with diameters ranging from 1 km to 50 km.  Calderas form as a result of collapse of a volcanic structure.

Eruptions of ash and pumice

Caldera collapse

Steam explosions

Today

Formation of the Crater Lake Caldera in Southern Oregon

CALDERA…

Crater Lake Caldera in southern Oregon is an 8 km diameter caldera containing a lake. 

SLOPE LANDFORMS

Slope Development Landforms and landscapes change over

time as a result of various dynamic factors. These factors include tectonic movement, weather, erosion, and gravity.

BUTTE

a prominent isolated hill with steep, often vertical sides and a small, relatively flat top

MESA A  (Spanish and Portuguese for "table") is the American

English term for tableland, an elevated area of land with a flat top and sides that are usually steep cliffs.

In Spanish such a landform is more usually known as a meseta.

Formed by weathering and erosion of horizontally layered rocks that have been uplifted by tectonic activity.

PLATEAU

another landform that is relatively level, and some sources claim that a plateau is an elevated plain.

A plateau has at least one steep, cliff-like side. It forms as a result of geologic uplift (the slow upward movement of large parts of stable areas of Earth's crust due to heat forces within the planet) or as a result of much lava flows that spread out over hundreds of thousands of square miles. 

CLIFFSa significant vertical, or near vertical, rock exposure. are formed as erosion landforms due to the processes of erosion and weathering that produce them.

usually formed by rock that is resistant to erosion and weathering. 

Sedimentary rocks are most likely to form sandstone, limestone, chalk, and dolomite. 

Igneous rocks, such as granite and basalt also often form cliffs.

ARTIFICIAL LANDFORMS  An artificial island or man-made island that

has been constructed by people rather than formed by natural means.

YAS MARINA ISLAND

 is an artificial island in Abu Dhabi, UAE near natural Sir Bani Yas island.

THE PALM JEBEL ALI

 is an artificial archipelago in Dubai, United Arab Emirates which began construction in October 2002, was originally planned to be completed by mid 2008 and has been on hold since

HARBOR ISLAND

 is an artificial island in the mouth of Seattle, Washington's Duwamish Waterway where it empties into Elliott Bay.

was then the largest artificial island in the world, at 350 acres (1.4 km²).

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