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106 HAS BEEN A FANTASTIC GEOGRAPHY CLASS !!! ALL THE BEST

Check out the volcanic bombs in the movie 2012!

Plate tectonics questions

I have written your questions in your exact words though there are spelling and grammar mistake. I will provide the answers in point form, please elaborate on the points yourself

Exam related qn:
Nameless: Do we have to memorize the different plates? Do we have to memorize the different volcanoes?
Ans: YES

Nameless: Will we have to draw out the diagrams of different plate movements during the exams?
Ans: NO

TOPIC : PLATE MOVEMENT
Nameless: What will happen to the plates when it transform?
Plates will slide past each other, no crust destroyed and no crust created

Nameless: Without the earth's core, what will happen to earth?

Earth scientists have theorized that the Earth's core is responsible for the planet's magnetic field as well as plate tectonics. Hence without the core, it might affect the magnetic field. The outer core's mobility also allows it to generate electrical currents.

Jia Heng: What is the core's temperature?

It is approximately 4000-5000 degree celsius.

Clester: Why will plates clash?
Plates do not clash! They move and collide due to the convection currents. Convection currents is caused by extreme heat from the Earths core, which heats up the magma. When the magma cools down, it sinks down towards the core, thus cause plates to move towards each other.

TOPIC: VULCANICITY
Tiffany/ Royden /Dillion/ Y XinYi  K Xin Yi: What is vulcanicity?
The movement of magma, both into the earth's crust and onto the earth's surface.

Amanda: Fold mountains and volcanoes are formed along?
Fold mountains and Volcanoes are formed along the plate boundaries.  A large number of earthquake are found along the pacific ring of fire too.

TOPIC: VOLCANIC ERUPTION
Bryan/ Vernon/ Y XinYi/ Zhiwei/ Danial: What causes an eruption? Why does a volcano erupts?
Dillion/ Vernon / Cleser : How are volcanoes formed?
When rock inside the Earth becomes hot enough it melts. This molten rock, or magma, is less dense than the surrounding solid rock, the relatively low density of the magma causes it to rise to the surface of the Earth. If the magma contains water and dissolved gasses, when the magma reaches the surface the water and dissolved gasses will suddenly expand into steam and gas, causing a violent eruption. This is like shaking a coke can and then popping the tab.

Jia Heng: What happens during an eruption?
The eruption process starts with pressure building up within a magma chamber below Earth's surface. Magma contains several dissolved gases. When the pressure on the magma is greater than the vapor pressure of the gas, it remains dissolved. If this pressure is disrupted, it can cause the gases to form small gas bubbles, known as vesicles, within the magma. The gas bubbles push to the surface because they are less dense than the magma. Some volcanoes erupt violently, causing massive destruction within minutes, whereas the magma of other volcanoes seeps out so slowly there is no harm done.

Joelle: Why the crater will be blown up?
This only occurs in volcanoes that have a violent eruption. With the immense pressure being built up within the magma chamber, the eruption becomes violent with a great force that blows the crater off as the gases escapes to the surface.
Tiffany: Is all volcano eruption the same like the amount of lava?
The amount of lava ejected varies in each eruption and thus may not be the same. It may be difficult to monitor the amount of lava that is ejected too.

TOPIC: FORMATION OF LANDFORMS
Dillion: How are landforms created?
Different types of plates movement creates different landforms. Fold mountains are formed when two plates move towards each other, forcing sedimentary rocks upwards into a series of folds. Ocean Trenches are formed when two plates collide. This can create a trench on the sea floor side and a mountain range on the side of the land mass, as can be seen with the Andes. Island Arcs are formed when an oceanic plate converges with another oceanic plate can lead to volcanoes being formed. Ocean Ridges are formed when plates move away from each other, creating a new crust as magma is pushed up from the mantle.

Zhiwei: What is the maximum number of volcano on earth?
There are no maximum numbers of volcanoes. In fact the number of volcanoes might not be accurately quantified. There are probably millions of volcanoes that have been active during the whole lifespan of the earth. During the past 10,000 years, there are about 1500 volcanoes on land that are known to have have been active, while the even larger number of submarine volcanoes is unknown. At present, there are about 600 volcanoes that have had known eruptions during recorded history, while about 50-70 volcanoes are active (erupting) each year.

TOPIC: VOLCANO STRUCTURE AND SHAPE
ChunKit: Will there be more than two opening?
Possible. But most volcanoes usually have 1 main vent (opening).

K Xin Yi: What is magma made of?
It is a mixture of molten or semi-molten rock, volatiles and solid. It also contain suspended crystals and dissolved gas and sometimes also gas bubbles.

Danial: What is the temperature of the lava of the volcano?
When first erupted from a volcanic vent, lava is a liquid at temperatures from 700 to 1,200 °C (1,292 to 2,192 °F). Up to 100,000 times as viscous as water, lava can flow great distances before cooling and solidifying

Hidayah: How far can lava spread?
 A lot depends on the viscosity of the lava, the terrain on which it is emplaced, and the rate at which it is being erupted to the surface. The longest recent flow in Hawai’i was erupted from Mauna Loa in 1859. It is about 51 kilometers long from the vent to the ocean (we don’t know how much longer it went out under water, but probably not too much farther). There is a lava flow at Undara in Queensland, Australia is 100 miles (160 km) long.

Amanda: What is the layers of ash and cinder?
Volcanic ash consists of fragments of pulverized rock, minerals and volcanic glass, created during volcanic eruptions. Cinders are extrusive igneous rocks. Cinders are similar to pumice, which has so many cavities and is such low-density that it can float on water. The colour of cinder is brown.

Chun Kit: How does it form to be steeper/gentler slope for volcano?
Volcanoes with basic lava flow tends to be gentler because the lava is more fluid, therefore it flows faster and spreads to a further area. Volcanoes with acidic lava flow is more viscous (thicker), therefore it flows slower and solidifies near the crater. Thus resulting in a steeper slope volcano.

Nameless: Why does volcanoes have a smelly smell?
It could be due to the sulphur (colourless gas with a pungent smell) that is released into the atmosphere. Hydrogen sulphide is also being released into the atmosphere, it is a Colourless, flammable gas with pungent smell of rotten eggs. Lastly Hydrochloric acid may also be released, it is a Colourless gas with an irritating, pungent odour. The vapour irritates the eyes severely, and may burn the skin.

Cynthia: Where does ash come from?
Rios: Why is there carbon dioxide or steam when released?
ChunKit: How can gases grow on volanoes?
The gases are stored underground, and could be trapped in rocks/magma/lava. The gases will be released durin a volanic eruption together with ashes, magma etc. It may also be released indirectly to the air by the ground water that are heated by volcanic action.

TOPIC: TYPE OF VOLCANO
Royden: What are the types of volcano?

There are 3 types of volcanoes: Active, Dormant and Extinct.

Cynthia/ Hidayah: Where can we find extinct volcanoes?
Rios:How does a volcano become extinct?
Tiffany: Why are there extinct volcanoes? Why wll magma get lesser?

A volcano is extinct if it remains dormant for 10,000 years. . If you deplete the magma chamber supplying the volcano, it will stop erupting and become extinct, and similarly if a hot-spot volcano moves away from the mantle hotspot causing the volcanism, it will become extinct. Another reason is the hotspot theory. A hotspot is located in the middle of a plate (below it). When the hotspot emits magma, it will form a volcano. As the plate moves, the volcano located on the plate moves together with it. It is then cut off from the magma source which is the hotspot, and it becomes extinct. The process
will then repeat itself.

Xuan Qi: Do the volcanoes in the same country erupts together?
Not neccessary. It depends on the location of the magma chamber. The volcano erupts right above the magma chamber, which is affected by the movement of the plates.

Nameless: How do  you know if a volcano is active or not?

An active volcano is currently erupting or is likely to erupt soon.

Nameless: How do we know if one volcano is dormant or extinct?
A dormant volcano is presently inactive, but may erupt in the future. However an extinct volcano is dead, and will not erupt again.

Amanda: Will plants grow on all extinct volcanoes?
Hidayah: Why do grass gorwn when volcanoes extinct?
Yes most of the extinct volcanoes will start to have vegetation growth due to the fertile soil that are suitable for crops to growth. Extinct volcanoes have already been dormant for 10,000 years. Therefore this is a sufficient time for vegetation to start regrowing again.

TOPIC: VOLCANIC IMPACTS
Y Xin Yi: What is the impact for those living near volcano?
Xuan Qi: How does the volcanoes help people?
Cynthia: Why do some people live near volcanoes even if it is dangerous? 

Eric/ Danial: What is the advantage of a volcano?
Scenic landscape to attract tourists, Fertile soil for crops to grow, Geothermal energy to produce electricity, Mining jobs

Zhiwei: Why is volcano so deadly?
During a volcanic eruption, houses, buildings, roads, and fields can get covered with ash. If the ashfall is really heavy it can make it impossible to breathe. Lava flows can run over houses, roads, and any other structures. Pyroclastic flows are mixtures of hot gas and ash, and they travel very quickly down the slopes of volcanoes. They are so hot and choking that if you are caught in one it will kill you. They are also so fast (100-200 km/hour) that you cannot out-run them.

Xuan Qi: Is there any symptoms before the volcano erupts?

Good Qn! Before a volcano erupts, there is normally an increase in earthquakes and tremors near and under the volcano. These are caused by magma (molten rock) pushing upward through the rock under the volcano. The ground may crack open and allow steam to escape. Gases such as carbon dioxide and hydrogen sulfide, a gas that smells like eggs gone bad, frequently are present and escape in seams along the mountain. Hot springs in the area around the volcano may appear or change in appearance and temperature.

Map readng Questions by 106

Mapreading

Qns:
Eric: 8 digit grip reference
Nameless: 6 number grid how to do?
Nameless: Teach me on Settlement and contour lines?

Miss ST:
I guess that you guys are referring to the 6 digit grid reference in mapreading.

1st and 2nd digit: Locate the 4 digit grid reference  identifying the square that the item lies in. Next read the HORIZONTAL LEFT digits.

3rd digit: Divide the horizontal line (within the square into 10 equal parts, then draw a dotted line down from the object to locate its number)

4th and 5th digit: Read the VERTICAL BOTTOM digits. It will always be the smaller number if you cant remember. 

6th digit: Divide the verical line (within the square into 10 equal parts, then draw a dotted line down from the object to locate its number)

Settlement patterns: refer to earlier posts.

Contour lines: Will discuss in class

Clester: How to find the bearing of a location?
Will go through in class.

Questions asked in class

1. How are whirl pools formed?

Basically, a whirl pool is a swirling body of water produced by the meeting of opposing currents.

If you are referring to the whirlpools in the oceans, they are usually caused by tides. However small ones can also be formed by other movements of water eg base of water falls where there is a narrow and shallow strait of fast flowing water.


2. What happens to the oceanic crust that has subducted underneath the continental crust?

The denser (heavier) oceanic plate sinks under the continental plate, and it will melt and turn into magma. The magma then rises upwards towards the earths surface, and is released through volcanic eruption. It is then called lava, which is what we see during an eruption.


Admin matters

1. Students that have dental appt (18 Sept) - a few of you left earlier for dental during the lesson. I went through the diagrams of the 3 types of plate movement (convergent, divergent and transform). Pls borrow your classmates worksheet and fill it in.

2. Homework : To complete worksheet on vulcancity by Thursday 20 Sept!

3. File check: I will browse through your files on 25th Sept 

4. Lesson venue: Pls assemble at the Xinnovate on the 25th Sept (Tues)

Class Quiz

There will be a class quiz next Tuesday on the 3 types of plate movements. Please revise and be prepared for it. Kindly disseminate the information to your class mates =)

Questions raised in class today

How thick is the earth's crust?

The oceanic crust is 5 km (3 mi) to 10 km (6 mi) thick^[1] and is composed primarily of basalt, diabase, and gabbro. The continental crust is typically from 30 km (20 mi) to 50 km (30 mi) thick and is mostly composed of slightly less dense rocks than those of the oceanic crust.



What happens to the oceanic crust when it is subducted under the continental crust?

Life cycle
Oceanic crust is continuously being created at mid-ocean ridges. As plates diverge at these ridges, magma rises into the upper mantle and crust. The youngest oceanic crust is at the oceanic ridges, and it gets progressively older away from the ridges.

The amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness (7±1 km). Very slow spreading ridges (<1 cm·yr^-1 half-rate) produce thinner crust (4-5 km thick) as the mantle has a chance to cool on upwelling and so it crosses the solidus and melts at a lower depth, thereby producing less melt and thinner crust.

The oceanic crust subducts at what are known as convergent boundaries. These boundaries can exist between 2 oceanic plates .

In the second situation, the oceanic plate always subducts because the continental lithosphere is less dense. The subduction process consumes older oceanic plate, so oceanic crust is seldom more than 200 million years old.^[5] The process of super-continent formation and destruction via repeated cycles of creation and destruction of oceanic crust is known as the Wilson cycle.