Monday, 25 November 2013

What made Typhoon Haiyan so Devastating?


Typhoon Haiyan, which devastated the Philippines in November, is one of the strongest storms ever recorded at landfall. So how did this typhoon come about?

Tropical storms (hurricanes, cyclones or typhoons, depending which part of the world you're in) can only occur when conditions are just right. These are the ingredients of a typhoon:

1.    Warm ocean water (at least 27C to a depth of 50m)
2.    At least 5 degrees/ 500km away from the equator where Corioli's force is strong enough to cause rotation (hurricanes rotate ACW in the northern hemisphere and CW in the south)
3.    An unstable/steep lapse rate (the change in temperature with height) to encourage convection
4.    Low vertical wind shear (the change in wind speed with height), which could prevent convection and disrupt the structure of the storm
5.    High humidity in the mid-troposphere (about 5km up)
6.    A tropical/easterly wave/disturbance (an area of low pressure with clouds and thunderstorms, around 100 develop every year but only 10 meet the right conditions to turn into a hurricane).

Even when all these conditions are met, a hurricane may still not develop. However, if it does, this is what happens:




But why was Typhoon Haiyan so devastating, what made it one of the strongest typhoons ever recorded?

Well, to start with a single hurricane vary in size and intensity, when they reach land they are often not at their greatest strength  (Katrina reached Category 5 on the Saffir-Simpson Hurricane Scale when she passed over the Gulf of Mexico but had fallen to a 3/4 by the time she reached Louisiana). Also, when they reach land and move away from their fuel source of warm water they quickly lose some of their strength.

However, you can see from the image below, it just so happened that when Typhoon Haiyan hit the Philippines it had reached it's peak intensity: a Category 5 with sustained wind speeds up to 200mph. Haiyan was able to reach this intensity because she formed over a wide expanse of open ocean with perfect hurricane conditions; one is that there was very little wind shear in the area to disrupt the convectional air flows and rotating winds.


The typhoon also had a plentiful supply of warm water, not just within the first 50m, but unusually (some have linked this to anthropogenically influenced climate change) the ocean was warm enough for hurricane formation down to a depth of 100m! Once the storm whipped up the top layer of water there was still a plentiful supply of heat below giving the typhoon more and more energy. Check out the map below:


Not only had this typhoon reached it's full strength when it hit the Leyte and Samar provinces of the Philippines but it brought a huge storm surge with it, which was magnified by a deadly combination of wind direction and coastal topography. Along most of the eastern side of the Philippines the ocean is very deep, making storm surges unlikely as waves need progressively shallow water to build any height. However, the orientation of Haiyan as she hit land meant that north-westerly winds drove the storm surge into San Pedro Bay which, although mostly deep water, becomes much shallower and also narrower to the north. The bay acted liked a giant funnel, causing the tsunami-like surge to reach 5 metres in height.



So far, the death toll is estimated to be over 5000, 600 000 are homeless, while the economic costs to the Philippines range from $5-14 billion. The super-strength and huge size of this storm (estimates of her diameter range from 6-800km) and the devastating surge it brought with it were bound to have a severe and lasting impact. But maybe if the archipelago has been better prepared the damage and loss of life could have been mitigated to some extent. Although some preparations were made (e.g. the evacuation of 1 million people and government announcements telling people to prepare), it was no where near enough. Firstly no one was expecting the storm surge so, for example in Tacloban several thousand people took shelter in a big indoor 'stormproof' stadium. Sure enough, the roof stayed on, but people were killed by the storm surge which flooded through the bottom.

The typhoon also hit one of the poorest regions of the Philippines, where people lived in flimsy make-shift shanty-towns and even properly built structures do not conform to an sort of typhoon proof regulations as they surely should do, being in a high risk area. Low levels of education and a corresponding lack of appropriate language grading by the authorities also meant that despite being warned about an impending storm surge many residents did not realise what this meant so failed to take even simple potentially life saving measures such as going upstairs in the stadium instead of staying on the ground floor until it was too late. On top of all this, the Philippines has a very high population density, over 300 people per square km, compared to around 250 in the UK, putting a huge number of people at risk.

In conclusion, a combination of physical and human factors, summarised below, made Haiyan one of the worst natural disasters we've seen in a long time.


  • Open ocean with no land masses
  • Very little wind shear
  • Very warm water down to 100m
  • Made landfall at full strength
  • Funnelling effect in San Pedro Bay
  • Lack of preparation
  • High population density


Lets just hope that some lessons are learned for next time. In the mean time, please donate generously to help the survivors. You can do so here.

Finally, check out this page which has some great maps explaining the path and impact of the typhoon as well as some before and after satellite photos:




References

http://www.theweatherprediction.com/tropical/
http://www.aoml.noaa.gov/hrd/tcfaq/A15.html
http://agora.ex.nii.ac.jp/digital-typhoon/help/world.html.en#id2
http://www.theweatherprediction.com/tropical/
http://en.wikipedia.org/wiki/File:Haiyan_2013_track.png
http://archives.starbulletin.com/2002/05/19/news/index2.html
http://scienceblogs.com/gregladen/2013/11/11/why-was-typhoon-haiyanyolanda-so-powerful-and-is-this-a-trend/
http://www.livescience.com/41025-typhoon-haiyan-most-intense-storm.html
http://www.economist.com/news/asia/21589916-one-strongest-storms-ever-recorded-has-devastated-parts-philippines-and-relief
http://www.dutchwatersector.com/news-events/news/8391-typhoon-haiyan-pushed-devastating-5-m-high-storm-surge-into-tacloban-city-philippines.html
http://www.usatoday.com/story/news/world/2013/11/22/philippines-typhoon-lessons-learned/3664883/
http://www.economist.com/news/leaders/21589883-responding-disaster-essential-so-preparing-next-stress-test

















Sunday, 24 November 2013

Level 3/4 Separatism Essay with Examiner Comments

Analyse the reasons for separatism within and/or across national boundaries and discuss its consequences (40 marks)

Separatism is an attempt by a regional group within a country or across the borders of one or more countries, to gain more political control from central governments over the areas in which they live. There are many different reasons for why separatism occurs around the world, these can include: the feeling of being economically depressed compared to other areas within the same country; the fact that some people feel that they are in a peripheral location to economic and political care; the desire to protect and build upon a minority language or religion and the feeling or being mistreated due to being an ethnic minority (e.g. the Tamil Tigers in Sri Lanka). Separatism can lead to a wide range of consequences that range from the collapse of governments and civil wars to, more political disputes and peaceful protests. Separatism does not have to be aggressive.

Good introduction to the topic, defines separatism and outlines the causes and consequences. It would be good to mention some real examples too, for example the case studies used in the essay could have been mentioned in appropriate places - see example in italics.


The Sri Lankan civil war is a prime example of where Separatism has led to aggressive consequences, in this case the acts of the Tamil Tigers (a separatist group) led to a civil war that spanned over three decades. The Sri Lankan civil war was fundamentally caused by ethnic discrimination between the ethnic majority Sinhalese and the Tamil minority that populated the north and northeast of the island.  When the British owned Sri Lanka they turned the country into the tea making capital of the world and brought with them a vast amount of wealth and benefits to certain groups. These certain groups where the Hindu Tamils of Sri Lanka and India; furthermore when the British gave Sri Lanka its independence it did not take long for tensions to arise. With the minority Tamils not gaining any political power when Sri Lanka gained its Independence, they were repeatedly repressed and eventually leading a group known as the Tamil Tigers to start an insurgency that would turn into a civil war (1983-2009). This conflict had many consequences. One of which was the massive amount of civilian casualties that occur during many attacks on both sides. During the entire war it is estimated that up to 70% of the 80,000-100,000 people that died in the war were actually civilian casualties. This huge social impact was just accompanied by war crimes such as rape and torture throughout the war and none more so at the end when the government shelled a hospital island and forced the fleeing Tamil civilians into imprisonment camps. 

Detailed knowledge builds a sense of place for the first case study, evidence of critical understanding and use of specialise vocabulary shown.


On the other hand it was not just the Sri Lankan government that were behind social impacts; the Tamils found themselves being listed as a terrorist organisation by 34 countries due to the suicide bombings they carried out. One of which was outside the world trade centre in the capital city of Colombo which killed 39 people and meant that many were scared to go about their day to day lives. These bombings also led to increased security in main towns and cities and made in increasingly harder for civilians to live a normal life.  However over the course of the war it there were not just social consequences; one environmental impact was the destruction of over 5 million tress. These trees used to supply wildlife with homes and shelters and thus a negative feedback system is being observed in some unique species within different regions in the north of the country. The destruction of these 5 million trees has not only had severe environmental impacts; it has also led to more farmers suffering from poverty as they are missing out of the economic benefits of the forest areas that so many relied on. Unfortunately for the Sri Lankan people and government, the poverty and negative feedback for the destructions of so many trees is not the only or worse economic impact due to the civil war. One of the worst impacts is the fact that the government is still spending up to 30% of its yearly budget paying for damages and the cost of the war (the war is thought to have cost the government $200 billion).

Continued use of detailed knowledge and critical understanding of this knowledge. Synopticity shown in the range of impacts that are mentioned (social/environmental/economic). Environmental impacts could be stronger - negative feedback system is not explained? 'Unique species' should be more specific - does the candidate mean endangered or endemic? Also some spag inaccuracies.


Another example of where Separatism has led to clashes is between the Kurds and the Turkish government (Turkish in particular). In this case the Kurdish people (an ethnic group by their own right, with their own language and traditions) do not have a nation and partition as well as fight for their own country of Kurdistan. The main issue here being that this Kurdistan would take a large chunk out of Turkey and some land out of countries such as Iran and Iraq. This and the fact that the Kurds have their own language and beliefs has led to them being continually persecuted and oppressed. A fine example of where war crimes have been committed against the Kurds is through a genocide by Saddam Hussein in the 90’s.

Second case study briefly outlined with some specific knowledge. Could be improved with more detail. The reason for using this case study is slightly unclear - what does it add to the essay? What point is it used to illustrate?


On the other hand, not all acts of separatism end up leading to aggressive conflicts. The partition by some people and governmental officials in Scotland, which includes the use of protests and voting, is a prime example of where separatism is being resolved peacefully. There are some within Scotland that believe that the only way to preserve and save their native language of Gaelic, is to leave the UK and become their own separate nations. To try and stop this from happening (many think due to the fact that there is oil off of the north coast of Scotland that the UK need) the English government offers financial and social support. This leads to clashes as the British people believe that it is unfair that for instance they have to pay for university tuition fees and the Scottish students too.

Use of 3rd case study this time backs up a point made - that the consequences of separatism are not always violent. This shows critical understanding of the issue. Somewhat unclear at the end. 


To conclude, it is easy to show how badly separatism can impact of both society, the environment and the economy in a country and across borders (Scotland). However in more cases than not it seems that it leads to violence as people struggle to have their voices listened to and thus lash out aggressively. This can be shown by the fact that Scotland and the UK have not had violent clashes, as their voices are being listened to and acknowledged.  I would also say that when looking at the Kurds and Sri Lankan civil war, it seems to be that the main consequences of separatism tend to be social. This in some ways could be said to be ironic and in many cases the causes of the Separatism in the first place is social issues. Finally is would seem that when looking at Scotland compared to example such as Sri Lanka; when there is a well-established government overviewing the whole scenario, it tends not to lead to aggression and thus the consequences are far less.

Strong conclusion discussing the consequences of separatism, however does not mention causes.
Overall the candidate has shown evidence of detailed knowledge, frequent critical understanding and some ability to synthesise a range of information. The case studies are rather imbalanced and the quality of the argument, whilst strong in places, could be structured a bit better, e.g. redundant use of Kurdish case study. However, overall a sound essay, high level 3 to low level 4.

1109 words - about the right length to write in an hour, maybe slightly too long.

By Sam Evatt

Monday, 18 November 2013

Level 3/4 Separatism Essay


Analyse the reasons for separatism within and/or across national boundaries and discuss its consequences (40 marks)

Separatism is an attempt by a regional group within a country or across the borders of one or more countries, to gain more political control from central governments over the areas in which they live. There are many different reasons for why separatism occurs around the world, these can include:

Saturday, 5 October 2013

What we really mean...

...when we write essays!


Friday, 27 September 2013

Climate, Energy and Politics

Some interesting discussion on climate change and UK energy issues (first 30 mins) in this week's 'Any Questions'

http://www.bbc.co.uk/programmes/b03bg4wg


Sunday, 15 September 2013

Ugly Animals are Important too!!

Conservation - should it apply to all animals and plants... or just the 'nice' ones? The unfortunate looking blobfish has recently won a competition to become the mascot of the Ugly Animal Preservation Society, who believe that it's not just pretty or cute members of the animal kingdom that are deserving of conservation efforts! Check out more info about it here and here. Poor little blobfish he looks so sad! Lets hope him and all his ugly friends don't die out any time soon, after all, I'm sure they have lovely personalities!




Tuesday, 3 September 2013

Immigration - Threat or Opportunity?

Radio programme today about immigration to the UK - great for Population Change at AS and Conflicts (Multicultural Societies) at A2. You can listen here:

Call You and Yours Tuesday 3rd September 2013


What on Earth is a Zeugen?!

'Not all students knew what yardangs were and there was some confusion with rock pedestals and zeugen' 


This quotation is from the examiner report on the June 2013 GEOG 1 exam, and I have to say I am glad to see it! Not because I am happy that students got it wrong, but because I hope it will help to solve the mystery of what a zeuge actually is, and perhaps open up a wider discussion on the flexibility of geographical terminology.

Tuesday, 27 August 2013

Youthful and Ageing Populations

I found these two very comprehensive videos on youtube on the UK (focusing on Devon) and The Gambia. We'll study Uganda in class but the underlying theory is the same and there are many similarities between Uganda and The Gambia in terms of the balance between population and resources.




Monday, 26 August 2013

Thoughts of an AS Geography Examiner



This summer I worked as an examiner for AQA and whilst doing so I thought it would be useful to write down some things I learnt about answering exam questions. Having to mark people down for silly mistakes or just basic lack of exam technique was painful at times! Unfortunately the way exams are these days means that a lot of it is about your ability to answer questions in the right way rather than how much geography you know. Obviously you need detailed geographical knowledge as well but I would say someone with less knowledge but better exam technique is going to come out with a better grade than someone who can reel off hundreds of case studies with supporting facts and figures and explanations.

I know it's a long way before the exams, we're right at the beginning of the year, but it's never too early to start developing good habits when it comes to applying your knowledge. Hopefully, with enough practise, you'll be so used to it that you can focus on the geography rather than trying to interpret the question and avoid making unnecessary errors that could cost you a grade. So, without further ado, here's some things I wrote down while marking.... I hope it helps! (nb this mainly applies to AS nothing about essays at A2 in there I'm afraid but much of it applies to both levels).

  • Don't write outside the area of the question (e.g. in the margin) if need more room use a separate sheet of paper and indicate this in your question, otherwise part of your answer will get cut off.

  • Write clearly in black ink, so many of them didn't scan properly or the handwriting was illegible

  • Answer needs to be very very focused on the question and command words, there is no point adding in random stuff that's not relevant to the question just to try and fill the space. If anything this is annoying for the examiner who has to trawl through trying to find the good parts of your answer.

  • Lists or bullet points or writing in note form will confine you to low level 1.

  • Study OS maps very carefully, e.g. in one questions people consistently counted the wrong number of churches and assumed that a 'place of worship' was a church, when in fact it could have been a mosque, synagogue etc. A-level lessons often do not have much time to spend on studying OS maps so this is something you should practise your own time too.

  • If asking to compare you MUST compare! Do it point by point, do not write 2 separate paragraphs and expect the examiner to compare for you!!

  • Please learn definitions correctly! This is the easiest thing ever, even if you don't understand it you can just memorise it and still get your 2 marks, 2 marks are not worth losing due to laziness. Ask your teacher for a list of key words/look in the textbook and start learning them now!

  • Think about things carefully and try not to oversimplify, e.g. renewable energy isn't always sustainable or good for the environment, the phrase 'three gorges' comes to mind...

  • I really can't be bothered to read illegible answers... (i did try of course, but you are not doing yourself any favours if the first impression your answer gives to an examiner is 'oh God, seriously? this is English??'). You know that exams are marked on the computer now, so imagine how illegible your illegible handwriting is going to be once it's scanned... then imagine that you and your 10 000 friends from the 'my hand writing is so illegible it looks like an alien code' society decided to sit the A-level geography exam.... 

  • Marking the same question over and over and over gets pretty boring, especially when everyone uses the exact same case studies from the exact same textbook... there's nothing wrong with being original and giving your own opinions occasionally (rather than the opinion of the guy who wrote the textbook), it might wake the examiner up from their marking stupor and encourage those sitting on the fence between levels to mark you up instead of down...

  • e.g. HIV in Botswana.... One child policy in China.... snore....these are great case studies if that's what you did in class, but please tell me something new or interesting about them

  • If the question asks you to discuss, please DISCUSS!!! don't just describe stuff, this is so tediously boring and sad to mark...(so much valuable and carefully learnt information... so carelessly regurgitated onto the page...) It was so uplifting when a student put in their opinion, compared two viewpoints, weighted up two situations, decided which negative impact was the least worst, considered short and long term, the past and the future, different aspects of something, variations in TIME/SPACE/SCALE etc etc and I could say, woohoo! they've reached the next level!

  • Saying there is a clear trend or lots of variation will not get you any marks, you must say what the trend is!! Duh!!

  • Few students seem to understand what 'implications for social welfare' means! And even fewer can comment on it 

    Learn what 'comment on' means and how this is different to simply 'describing'.

  • Using a black fine liner was clearer than a biro, and please don't write so microscopically tiny as exam scripts aren't scanned in HD.

  • Don't cross stuff out unless you're 100% sure! It could be right...

  • When comparing stuff 'A is 20% and B is 30%' is NOT a comparison! You need some comparing words such as 'whereas... only....much lower at...' in there!



Thursday, 15 August 2013

Smiles and Tears

Results day tends to bring about one of 3 reactions...


1) Joy and relief that you've achieved the grades you worked hard for (perhaps you were one grade off but you still got into uni)

2) Disappointment and distress that you haven't achieved what you were hoping for, despite working hard. Or your fears of failing after all those lessons you missed due to your personal circumstances have come true.

3) Disappointment and distress at the realisation that spending all year partying/procrastinating/being otherwise distracted or just lazy has resulted in you failing/doing rubbish in your exams.


If you were in category one today (as some of my A-level students were) CONGRATULATIONS!!!!!!!!!! =D. Or as I like to say, WOOOOO YEEAAHH!!!!

Feel free to dance around the room, hug random strangers (please stay away from anyone who is too strange looking) or eat an entire chocolate cake in one sitting. You could even have a revision notes bonfire but your notes are probably too precious to consider doing that and you probably plan to keep them neatly filed away for at least the next fifteen years until you're forced to get rid of them to make space for your new baby! Whatever you do, make sure you enjoy a well deserved celebration, you should feel very proud of yourself! I hope this inspires you to continue your hard work and success into the future.



If you're in the second group (which others of my students unfortunately found themselves in today), please try not to feel too upset. Take a step back and try to look at things objectively. If you were hoping to go to university is this still an option? You might not have got your first choice but do you have a back up or could you get in through clearing? Maybe this is a sign that A-levels aren't for you and you'd be more successful at something else? Or maybe you know exactly what you want to do and you need better grades to achieve it so the only way is to retake the year? If so, a year might seem like a long time, but don't despair! Think of what else you can do in this year (work experience, save up money, extra curricular activities) and how good your grades could be at the end. Lots of people have a year (or more) out and it ends up being a positive thing. You'll be more mature and more prepared for uni. Whatever happens, perhaps it's a 'blessing in disguise', maybe if you had got the grades you wanted and got into the uni you wanted you would have hated it or something worse would have happened to you. I know this is hard to believe right now but often things that we think are bad actually lead to something good, and vice versa. Just remember, don't give up! you can do it if you try!! A-level students, feel free to contact me for advice and I will try to help if I can!




Finally, if you are feeling upset about being in group number 3, (I hope you're not one of my students!) well, so you should be!! I'm afraid I don't have much sympathy for you. However, if you are now regretting your indolence and resolving to turn over a new leaf, I fully support you, that is admirable, if you really mean it. I hope you have learnt from your mistakes and won't repeat them! If you really do mean to change make a plan, get some help, get organised, make a real effort this time. Good luck!

Friday, 9 August 2013

Billboards and Camanchaca

Browsing facebook again and I noticed a headline 'Drinking Water out of Air' (check out the video below). Intrigued I read how a group of engineers in Lima have designed a billboard that captures humidity from the air to provide clean drinking water in city where many people don't have clean running water and much of the water they can get hold of isn't suitable for drinking.



As with anything the system isn't perfect. it requires electricity to run (perhaps solar panels could be installed? take advantage of the sun as well as the humidity!), it must be expensive to install (this could be funded by whoever had their adverts displayed on the board) and require some type of maintenance (though perhaps local people could be involved in this?) and unfortunately many areas around the world with water shortages probably don't have high enough humidity, but overall it's great to see innovative solutions to environmental challenges being tried and tested.

It reminds me of 2 things we study in the Deserts unit at AS. Further south along the coast from Lima a more low-tech solution to water shortages in the Atacama desert, Chile, has been successfully used to for some time to make agriculture possible in one of the driest places on earth.

© Laurent Abad (Flickr) 

Years can pass by at a time without rain falling in this area, yet near the coast the Humboldt current cools the warm air above it producing the camanchaca (love that name it sounds so descriptive), clouds of fog which blow over the land in the mornings like white blankets. They not only look beautiful but allow plants, and animals such as guanacos to survive in an area that would otherwise be too dry.


The other thing it reminded me of was another example of environmental engineering that was proposed as a solution to mitigate desertification in the Sahel (last video for this post I promise!).




All this almost makes me wish I'd done engineering! I'm not sure if they're planning to actually try this out but apparently the 'Great Green Wall' initiative has already been started so perhaps this will be tried in combination if anyone can ever get it together to undertake such a huge project in such a hostile environment. If the project is successful it could have a huge positive impact in one of the poorest more insecure regions in the world. 



Thursday, 8 August 2013

Baby BOOOMMMM!!

Normally when you hear 'UK' and 'Baby Boom' in the same sentence you assume I'm explaining the bumps on our population pyramid and referring to the one that happened after the last world war, but turns out from 2011-12 'one' became 'one and a half' born every minute.

You can see more details in this link: http://www.bbc.co.uk/news/uk-23618487

Great if the UK is one of your population policy case studies as this will give you something to say in those tricky 'assess the success' questions...


And here was me thinking that there'd always been loads of babies everywhere and I was only recently noticing it after having one myself, but perhaps I have become an unwitting victim of the very policies I've been teaching about!


MISSING: 60 Million Girls

Someone posted this link on Facebook today. Mention gender imbalance and most people think of China, but according to this article in some places in India there are only 3 girls to every 10 boys. In total it is estimated that there would be an extra 60 million women in India (the entire population of the UK) if it were not for sex-selective abortions, female infanticide, sex selective neglect or even murder.


Seems hard for us to comprehend how such attitudes of ignorance still prevail in some places of the world, so strong are people's beliefs they are willing to kill over them. We really are lucky to live in a largely tolerant and peaceful society. I really hope that one day people all over the world will get to enjoy the freedom and security that we do.

http://m.aljazeera.com/story/201372814110570679


Tuesday, 6 August 2013

Resources

Please check out the resources I have for sale and for free and leave me some feedback at this website:

http://www.teacherspayteachers.com/Store/Geogarific

About this Blog

Hi there! I'm Hafsa/Miss Hafsa/Mrs. Garcia and I love GEOGRAPHY and TEACHING. I decided to create this blog to support my A-level Geography students who are studying the AQA exam board, so this blog would be particularly useful for other AQA Geography students.

I use it as a place to showcase student work, to link interesting articles I find online and sometimes to write my own and. I want to encourage my students to look beyond the textbook and encourage others to become interested in Geography too.

Geography was always my favourite subject at school; studying the amazing natural landscape, examining how people interact with their environment, being outside in the field, understanding how natural processes work, finding out the real story behind the news headlines.

I decided to study Geography for 4 years at university, after which I wanted to carry on using my subject and sharing my passion for it in my every day life, so teaching, in particular A-level teaching seemed the perfect way to do this.

I hope you find this blog helpful, if you have any questions or comments please don't hesitate to contact me using the comments section below.







Sunday, 14 April 2013

Logarithmic Graphs

What is it? A graph with a logarithmic scale, one which increases by multiplications in value rather than additions (e.g. 1, 10, 100, 1000 rather than 1, 2, 3, 4). The value by which the scale is multiplied by is usually 10 (i.e. log base 10). Both scales may be logarithmic or just one (semi-logarithmic graph). Semi-logarithmic graphs normally have time displayed on x


Benefits? Useful for studying data that changes exponentially. Can display a much larger range of data than an arithmetic scale. Allows one to see increased detail at smaller values, while larger values are compressed. Small values occupy a larger proportion of the scale in comparison with larger values. On an arithmetic scale, unless the graph paper was very large, the smaller values would appear too small to see properly. Allows comparison between trends in small and large values

Useful for showing rate of change. A steep gradient shows a fast rate of change while a shallow gradient represents a slowing rate of change.

A constant proportional rate of change (an exponential change) is represented by a straight line on a logarithmic graph (rather than a curved line on a arithmetic graph). This means logarithmic graphs are good for comparing rates of change.


Limitations? Zero cannot be plotted. Positive and negative values cannot be plotted on the same graph. Can be difficult to draw and interpret as scale is distorted.


Uses in geography? 
Studying population data e.g. as in Gapminder
The Hjulstrom curve. 
The Richter magnitude scale/The Moment magnitude scale 
Magnitude-frequency flood risk analysis.



Example 1 (Logarithmic)







Example 2 (Semi-logarithmic)
nb - in this graph the scale is multiplied by 2 each time rather than 10 (i.e. log base 2).






Further information
Check out this video for a great explanation of logarithmic scales!
You can also find an introduction to logarithms here

Friday, 12 April 2013

The Formation of a Meander

Sometimes I find poems helpful for remembering things! So here's one I wrote about meanders, which includes lots of key geographical words you should be using to describe them!

Rivers always take the path of least resistance
Winding round obstacles into the distance
Even in straight channels bars of sediment seem to form
Alternating deep and shallow sections is the norm’
At alternating intervals of 5-7 times the bend*
The bars deposited when low flow conditions tend
Riffles and pools are they names these features go by
Weaving in between then, the thalweg must comply.

Riffles will reduce the river’s efficiency
Slowed by friction the water has no energy
To carry its load, so it drops it right there
Forming what’s known as a slip-off slope or point bar
While the inner bend is built up by deposition
On the outer bend the river’s flowing fast with a mission
The high hydraulic radius in pools is the reason for
Undercutting by abrasion and hydraulic action more.

This process is perpetuated by helicoidal flow
A corkscrew like movement about which you need to know!
This erodes the river cliff of one meander’s outer bend
Depositing downstream in the next one’s inner bend
As these processes continue the meander slowly migrates
Moving both laterally and downstream at a steady rate.



* 5-7 times the width of the channel – I wrote ‘bend’ because width’ didn’t rhyme!

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