KQ2 Notes PDF

Regent Secondary School Upper Secondary Geography 1 Topic: Living with Tectonic Hazards- Risk or opportunity? Gateway 2: What landforms and associated tectonic phenomena are found at plate boundaries? Geographical concepts  Tensional force  Compression force  Folding  Fold mountains  Rift valley  Block mountain  Volcano  Pacific Ring of fire  Shield volcano  Stratovolcano  Composite volcano  Crater  Vent  Magma Chamber  Magma  Lava  Viscosity  Geothermal energy  Earthquake  Focus  Epicentre  Richter scale  Aftershocks  Tsunami  Vulcanicity Learning outcomes (You will be able to): 1. Discuss how plate movements influence the general distribution of landforms and associated phenomena 2. Describe the characteristics of landforms and phenomena associated with the plate movements 3. Explain the causes of landforms and phenomena associated with plate movements 4. Describe the structure of volcanoes 5. Explain the shape and size of volcanoes 6. Describe the benefits and risks of living in volcanic areas 7. Discuss the impact of earthquakes on people living in areas prone to natural hazard Skill: Draw annotated cross section of a volcano Skill: Draw labeled diagrams to show formation of Fold Mountain, rift valley, block mountain and volcano

Regent Secondary School Upper Secondary Geography 2 Landforms found at plate boundaries The movement of plates at different plate boundaries can result in various landforms such as Fold Mountains, rift valleys and block mountains and volcanoes Fold Mountains Examples: The Himalayas, Rocky mountains and the Andes • Fold mountains are formed along convergent plate boundaries • The compressional force causes the layers of rocks to buckle and fold. • This process is known as folding. • The upfold is called the anticline and • The downfold is the syncline. • When there is increasing compressional force on one limb of a fold, the rocks may buckle until a fracture forms. • The limb may then move forward to ride over the other limb • Over millions of years, layers of rocks when compressed and folded form fold mountains • Folding is more common in sedimentary rocks as they are more flexible

Regent Secondary School Upper Secondary Geography 3 Rift valleys and block mountains  Formed at divergent plate boundaries  When plates pull apart, it gives rise to faults- a fracture in the rocks along which the rocks are displaced.  The tensional forces from the movement result in parts of the crust being fractured. This process is called faulting. A rift valley is a valley with steep sides formed along fault lines. E.g. East African Rift Valley (divergent movement of Somalian boundary and Nubian boundary of the same African Plate. A block mountain is a block of land with steep sides. It is formed when sections of the crust extend along fault lines and rock masses surrounding a central block sink due to tensional forces.

Regent Secondary School Upper Secondary Geography 4 Note the difference between faulting and folding! Folding Faulting 1. Caused due to horizontal movements. 2. Forces move towards a common centre. 3. Due to compression, different types of folds are formed. 1. Caused generally due to vertical movements. 2. Forces move away from the common centre. 3. Due to tension, faults occur along which displacement of rocks take place Volcanoes • A volcano is a landform formed by magma ejected from the mantle onto the earth’s surface • Magma is molten rock found below the earth’s surface and builds up within the crust to form a magma chamber • Magma that is ejected onto the surface is known as lava. • Upward movement of magma both into the earth’s crust and onto the earth’s surface is known as vulcanicity • Parts of a Volcano • Magma chamber- a reservoir of molten rock beneath the earth’s rust • Vents- openings in the earth’s surfaces with a pipe leading up around the vent to form a volcano • Crater- bowl-shaped geological formation at the top of a volcano • Calera- a large crater caused by the violent explosion of a volcano that collapses into a depression

Regent Secondary School Upper Secondary Geography 5 How volcanoes are formed Magma from the magma chamber rises to the surface through the vent. Magma is ejected onto the earth’s surface as lava Lava builds up around the vent, solidifying to form a small volcanic cone. The bowl -shaped opening is called the crater The summit of a volcano may be blown off during an explosive eruption. The sides of the crater collapse inwards due to the loss of structural support. As a result, a large depression known as caldera is formed. When a volcano erupts, lava, ash and rock fragments are released. The force of the volcanic eruption depends on the amount of pressure and gas in the magma During the formation of the volcano, the vent may become blocked. This forces the magma to find a new exit route to the surface. A secondary cone of newer volcanic material will then develop. New eruption of lava covers the ash layer and builds up the volcano Cross section of volcano

Regent Secondary School Upper Secondary Geography 6 Shapes and sizes of volcanoes • Volcanoes vary in shapes and sizes due to the characteristics of the lava Lava Low- silica High-silica  Low viscosity  Less explosive volcanic eruptions  Allow gases to escape easily  Flows more easily through the vent before reaching the surface  Outer layer of cooling lava forms a thin crust on the earth’s surface  High viscosity  Traps gases more easily  As magma rises towards the earth’s surface, the gases expands and causes an outward explosion  The volcano ejects lava, ash, rock fragments and gases Viscosity refers to the stickiness of the lava or resistance to flow Stratovolcanoes Shield volcanoes • Gently sloping sides and a broad summit • Low-silica lava flows easily and spreads out over a large area before solidifying • Eruptions are usually not explosive, with successive eruptions, the base of the volcano increases in size as lava accumulates • Common near divergent plate boundaries where magma can rise directly from the mantle • E.g. Mount Washington, USA • Steeper at the top, gentler at the base • High silica lava solidifies faster near the top • Develops from successive eruptions of lava and ash (may contain coarser rock fragments too) • After the initial eruption, subsequent eruptions ejects lava which covers the soft ash and prevents it from being eroded away • Over time, successive eruptions build a high volcano with slightly concave profile • Secondary cones may develop as magma from the vent seeps into sides of the cones and erupts • E.g. Mount Merapi, Indonesia

Regent Secondary School Upper Secondary Geography 7 Shield Volcano Strato- Volcano

Regent Secondary School Upper Secondary Geography 8 Volcanic eruptions may result in pycroclastic flow and lahars: Pyroclasts Lahar  Pyroclasts refer to hot rock fragments and super heated gases ejected during a volcanic eruption.  The movement of such rock fragments and gases down the slopes of an erupting volcano is known as pyroclastic flow  Refer to a mixture of pycrolasts and melted ice fro the mountains  Wet volcanic debris flowing down the slopes of an erupting volcano Pacific Ring of Fire  Where most active volcano activity occurs  Large number of earthquakes and volcanic eruptions occur along the edges pf the  Found along the boundaries of several converging plates- the Pacific Plate, Nazca Plate, The Philippine Plate, Australian Plate and the Eurasian Plate  There are volcanoes where tectonic plates are diverging too  Th