Water Features! 5th May ’09

This was Ms Tang’s second last lesson with us, and it was the one of the few times when I actually paid extra attention to the lesson, partly due to the fact that I had to do this blog post. However, I found this lesson rather interesting, when we learnt about waterfalls and rapids. This was what we learnt…

The formation of waterfalls: As water flows over the bedrock, the less resistant (‘soft’) rocks erode first. As the less resistant rocks keeps eroding, the gradient of the slope gets steeper, thus the formation of waterfalls. There is usually a plunge pool at the end of the waterfall, due to the force of the water hitting the bottom.

The retreat of waterfalls: Eventually, the more resistant (‘hard’) rocks will start to erode, thus the gradient gets less steep. However, the main cause of the retreat of waterfalls is the collapsing of the overhanging hard rock due to the erosion of the soft rock.







The formation of rapids is almost similar to that of a waterfall. The ground consists of alternate layers of ‘hard’ and ‘soft’ rocks, with the ‘soft’ rocks eroding first, thus forming a ‘step-like’ structure that resembles a mini waterfall.



Reflections:

Learning about the formation of these natural wonders is rather interesting. It seems so well planned yet it is a natural process, thus I enjoyed the lesson thoroughly (it’s my first time complimenting on Geography). Lesson was as usual, in a hot and stuffy classroom, everyone was noisy while the two groups were presenting on their respective topics. I finally realized that geography is actually a subject which ‘makes sense’. For instance, the steeper a slope of the waterfall, the faster/more the water flows, thus the formation of a waterfall…etc.

-Kevin (finally...)

2 May 2009

Hi 04, let’s revise what we have learnt from the previous lessons.\



*Three types of load:



*Erosion processes:
Corrasion (abrasion): the current picks up materials and rubs them along its banks and bed  the river erodes both horizontally and vertically
Attrition: The rocks collide with each others and break into smaller pieces, and become more rounded
Solution (corrosion): The word solution is used for both transportation and erosion process, but their meanings are slightly different. Solution in transportation means that the substances are just in the water, no chemical change; whereas when we talk about solution in erosion process, they will not be the same. (e.g. in the booklet: “Water contains dissolved CO2 from the air and this may react with limestone and chalk, causing it to dissolve).
Hydraulic action: the sheer force of water pushes into cracks at the river bank and the bank will gradually collapse

* Hjulstrom curve: a graph which shows the relationship between current velocity and particle size

The first line is the critical erosion velocity line: minimum current velocity before the particles are eroded.
The second line is the critical deposition velocity: minimum current velocity before the particles are transported.
Generally, when bigger the particle, the greater velocity needed to pick it up (transport) or erode. Very small and light substances like clay are very easily carried along by the current. However, because the clay particles tend to stick together, it requires higher velocity for the particles to be eroded.

Reflection:
As we gained more knowledge about Geography, I think that we are learning more of the “what” than the “how”. The knowledge in physical Geography is not so hard to get, since we are just accepting everything as fact. I feel like we are trying to make sense of common senses, in a more logical way, and ‘simpler’ way. At the basic knowledge of physical geography, the scientists mainly worked on putting our common knowledge from nature in to a neater and more organized table, for us to see the connection between them, and then make up even more connections (which we need to do ourselves).
I think that most of us would find it kind of boring to keep learning the “what” for so long. However, if we can link the knowledge together in a big picture, it would feel like using Lego to build a model of our nature, with more and more pieces after each lesson :).
I agree with Tung that ‘how’ is more important than ‘what’ (even though he was talking about different things anyway). However, ‘what’ is fundamental. If we don’t know what the problem is, it will be very hard to figure out how to solve the problem.
So, for the time being, let's enjoy Lego! :)

By the way, as I searched the internet, I found this website which contains a lot of useful presentation slides that we can use for our references:
http://www.slideshare.net/maliadamit/river-presentation-presentation (it has a mind map at the start, linking the river processes to different landforms, and then presents the knowledge accordingly)
http://www.slideshare.net/jacksonthree/river-processes-and-landforms (very long slides and I don’t really get the flow of the presentation, but I found it interesting because it has a lot of pictures in real life)
There are also similar slides in the website, hope you find this useful.
And enjoy the rest of weekend!!!
Jenny