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The Physical Geography Thread

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  • 27-05-2010 12:53am
    #1
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭


    Alright folks,

    Thought a thread specifically dealing with physical geography stuff might be interesting. Going through college (didn't do Geography for the Leaving Cert) Physical Geography was almost nearly avoided by most people and the ones that did it usually aimed to scrape a pass. So, a thread for general or more specific queries, e.g.:

    "What the hell is Physical Geography?"
    "What the hell is Geomorphology?"
    "Why are we doing maths again in Geography?"
    "Whatever happened to 'Old', 'Middle' and 'Youthful' stages of a river?"
    "What the hell is Manning's Roughness Coefficient?"
    "Can someone explain what foraminifera are and why are we learning about them?"
    "What's an isotope?"
    "How does carbon dating work?"
    "What's a Milankovitch Cycle?"

    Etc... etc... etc...

    So if you're in school or college studying Geography, or you're just an enthusiast (Alfred Wegener was a Geology enthusiast and he changed the world of Geology) or you've a question that neither Yahoo can answer and Wikipedia is unnecessarily complicated about, then come here!

    If any mods would like to stick this then that would be great.


«1

Comments

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    #2
    sheeplover
    Registered Users Posts: 49 ✭sheeplover


    Wow thank you for having opened this topic!
    I love geography and physical geography even if I studied other things at the college :)


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    #3
    Chewbacca.
    Closed Accounts Posts: 190 ✭✭Chewbacca.


    [HTML]Can someone explain what foraminifera are and why are we learning about them[/HTML]
    I would like to hear about this, and in fact all of the subjects above :pac:


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    #4
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭El Siglo


    Chewbacca. wrote: »
    [HTML]Can someone explain what foraminifera are and why are we learning about them[/HTML]
    I would like to hear about this, and in fact all of the subjects above :pac:

    Here's an explanation of foraminifera.

    Here's how I'd use them: "Intertidal foraminifera are well suited as sea-level indicators due to their quantifiable relationships with tidal heights" (Massey et al., 2006).

    And here's how that's done.

    All the rest, you can google.:pac:


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    #5
    Chewbacca.
    Closed Accounts Posts: 190 ✭✭Chewbacca.


    El Siglo wrote: »
    Here's an explanation of foraminifera.

    Here's how I'd use them: "Intertidal foraminifera are well suited as sea-level indicators due to their quantifiable relationships with tidal heights" (Massey et al., 2006).

    And here's how that's done.

    All the rest, you can google.:pac:

    Can these foraminifera microfossils be found in limestone areas like the burren?
    What exactly are they shelly-things with something like a little slug inside?
    Did you ever conduct research in this area?


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    #6
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭El Siglo


    Chewbacca. wrote: »
    Can these foraminifera microfossils be found in limestone areas like the burren?

    Yes in limestone, but I'm not sure of the Burren.
    What exactly are they shelly-things with something like a little slug inside?

    A periwinkle?
    Did you ever conduct research in this area?

    I'm doing my MSc on stable isotopes for sea-level analysis so I'll have to do a bit of foram stuff (counts and classification).


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    #7
    Chewbacca.
    Closed Accounts Posts: 190 ✭✭Chewbacca.


    El Siglo wrote: »






    I'm doing my MSc on stable isotopes for sea-level analysis so I'll have to do a bit of foram stuff (counts and classification).

    Is it the ratio of Oxygen 18/Oxygen 16 isotopes you are interested in to determine climate change over the years?


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    #8
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭El Siglo


    Chewbacca. wrote: »
    Is it the ratio of Oxygen 18/Oxygen 16 isotopes you are interested in to determine climate change over the years?

    No that's the palaeo stuff of deep sea forams, very interesting so it is but I wouldn't have time for it (thesis is due in on the 17th of September and I'd need to have been on the MV Celtic Explorer with a good research grant!). I'm doing a small section on foram counts and classification in surface sediments, the isotopes I'm concerned with at the moment are δ13C, δ15N and C/N ratios (stable isotopes).
    What this involves essentially is that I collect surface sediment (with a trowel) and plant material from an estuary along a line transect going from the terrestrial area right into the tidal mudflats (high altitude to low altitude), look at the isotopic variation along the line transect. The isotopic variation will change along the line transect and this gives me a clear (theoretically anyway) indication of recent sea-level in this particular area (marine isotopes differ from terrestrial so there should be a clear border between the two). This operates the same logical framework as foraminifera, i.e. certain numbers and species of forams are associated with certain tidal and flood conditions relative to sea level and the correlation with tidal height provides a tool for sea level analysis.
    The palaeo stuff works in the same manner instead you collect sediment with a core, usually going down 4 metres, date it (14C and 137Cs dating i.e. radiogenic isotopes and radiometric dating) and then you look at forams with in the strata, do counts, classify etc... and from this you should be able to reconstruct sea-level. Where there are no forams (this has happened before) you do stable isotopes.
    Hope that helps!:D


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    #9
    NotCarrotRidge
    Registered Users Posts: 160 ✭✭NotCarrotRidge


    Chewbacca. wrote: »
    Can these foraminifera microfossils be found in limestone areas like the burren?
    What exactly are they shelly-things with something like a little slug inside?
    Did you ever conduct research in this area?

    Yes, you can find forams in the Burren. They're very useful for dating the limestones in Ireland in general.

    The shelly things are probably gastropods or brachiopods.


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    #10
    eyescreamcone
    Banned (with Prison Access) Posts: 2,562 ✭✭✭eyescreamcone


    Can any of you 'geoga' experts help me settle an argument with my brother.
    I think Bantry Bay in County Cork is a fjord
    He says it's not

    Who buys the next round?


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    #11
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭El Siglo


    eyescreamcone wrote: »
    Can any of you 'geoga' experts help me settle an argument with my brother.
    I think Bantry Bay in County Cork is a fjord
    He says it's not

    Who buys the next round?

    I'm afraid to say you're buying the next round!:D You're brother is indeed right, Bantry Bay isn't a fjord, it's a ria. A ria is a coastal inlet formed by the partial submergence of an unglaciated river valley. So it's a drowned river valley that remains open to the sea. They're shorter and shallower than a fjord and are fairly well common in the southwest of Ireland and Bantry is a text book example.


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    #12
    eyescreamcone
    Banned (with Prison Access) Posts: 2,562 ✭✭✭eyescreamcone


    Thanks for that El Siglo :( haha
    Are there any examples of fjords in Ireland so?
    Are all fjords formed by glaciers?


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    #13
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭El Siglo


    eyescreamcone wrote: »
    Thanks for that El Siglo :( haha
    Are there any examples of fjords in Ireland so?
    Are all fjords formed by glaciers?

    About three as far as I can remember; Carlingford Lough, Killary Harbour and Lough Swilley. Yeh the glacier will carve out a fjord from a pre-existing channel, forming a 'U' shaped valley.


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    #14
    muckish
    Registered Users Posts: 610 ✭✭✭muckish


    I think only killary is the only genuine fjord in Ireland. Lough swilly looks like a fjord on the map, but doesn't have the classic shallowing at the mouth of the inlet. Dont know anything about Carlingford and have never heard of it being described as a fjord. Though if i'm wrong i'll gladly eat humble pie in the knowledge we have more than 1 on this isle!


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    #15
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭El Siglo


    muckish wrote: »
    I think only killary is the only genuine fjord in Ireland. Lough swilly looks like a fjord on the map, but doesn't have the classic shallowing at the mouth of the inlet. Dont know anything about Carlingford and have never heard of it being described as a fjord. Though if i'm wrong i'll gladly eat humble pie in the knowledge we have more than 1 on this isle!

    Carlingford Lough and Lough Swilly are definitely fjords, this paper shows where the ice sheet carved out Carlingford Lough and this paper states Lough Swilly is fjord. So we definitely have three confirmed fjords in Ireland.


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    #16
    muckish
    Registered Users Posts: 610 ✭✭✭muckish


    Pie_01.JPG
    Gladly eat it as I'm very pleased that Lough Swilly is a Fjord. I think this is something that could be used in some geo-tourism notes. So in essence that would make Lough Swilly the longest fjord in Ireland


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    #17
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭El Siglo


    muckish wrote: »
    Pie_01.JPG
    Gladly eat it as I'm very pleased that Lough Swilly is a Fjord. I think this is something that could be used in some geo-tourism notes. So in essence that would make Lough Swilly the longest fjord in Ireland

    Ah, all is fair in love and Geomorphology!;)


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    #18
    niamhhumag
    Closed Accounts Posts: 3 ✭niamhhumag


    hey i am new to this so im not sure if im posting this right but i am just enquiring to know has anyone sample answers for geography questions on human and regional? as much questions as ye have that have being marked an correct


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    #19
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭El Siglo


    niamhhumag wrote: »
    hey i am new to this so im not sure if im posting this right but i am just enquiring to know has anyone sample answers for geography questions on human and regional? as much questions as ye have that have being marked an correct

    Not here, this a general discussion forum for Geography and at that Physical Geography. Better off going to the Leaving Cert forum.


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    #20
    HavingCrack
    Closed Accounts Posts: 2,847 ✭✭✭HavingCrack


    As a geography student I'm a tad embarressed asking this but I've never managed to get an answer I'm happy with :o.

    What causes earthquakes away from faultlines? I've heard mining, old plate boundaries etc. all put forward but I've never been satisifed.


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    #21
    feicim
    Closed Accounts Posts: 289 ✭✭feicim


    Hi, good idea to have a Q&A thread.

    Can anyone tell me the pros and cons of radiometric vs oxygen isotope analysis and what each one is mostly used for?

    Thanks


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    #22
    feicim
    Closed Accounts Posts: 289 ✭✭feicim


    HavingCrack wrote: »
    As a geography student I'm a tad embarressed asking this but I've never managed to get an answer I'm happy with :o.

    What causes earthquakes away from faultlines? I've heard mining, old plate boundaries etc. all put forward but I've never been satisifed.


    I wouldn't have thought you can really get earthquakes away from faultlines. The area would need to be near a fault line of some sort, even a very old mostly inactive one.

    The only thing I could think of is maybe a large meteor strike.. or maybe nuclear bomb testing. I think they would show up on a richter scale.


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    #23
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭El Siglo


    Earthquakes can only occur on fault lines, and if there aren't fault lines present then it's usually on an inactive fault line as feicim mentioned.
    feicim wrote:
    Hi, good idea to have a Q&A thread.

    Can anyone tell me the pros and cons of radiometric vs oxygen isotope analysis and what each one is mostly used for?

    Thanks

    Oxygen isotope analysis is that of δ18O relative to δ16O, where the enrichment of δ18O means that the weather was colder (i.e. cloud condensation and precipitation was easier as the water molecule was slightly heavier) and δ16O where the weather was warmer (water was lighter, easy to evaporate something that's light, harder to condensate). The technique as far as I can recall is used mainly to look at glaciations, Heinrich events, Dansgaard-Oeschger events etc... It's not specifically a dating technique as the isotopes involved are stable (i.e. don't change over geological time), it can however be used to infer dated events from sequence stratigraphy (MIS5 etc...). 14C is the radiometric dating of carbon, used to date organic material from the last 50,000 years or so. It's good for dating but it's needs to be calibrated. Also, it can only be done on organic material etc...


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    #24
    NotCarrotRidge
    Registered Users Posts: 160 ✭✭NotCarrotRidge


    HavingCrack wrote: »
    As a geography student I'm a tad embarressed asking this but I've never managed to get an answer I'm happy with :o.

    What causes earthquakes away from faultlines? I've heard mining, old plate boundaries etc. all put forward but I've never been satisifed.

    El Sig and Feicim are correct. An earthquake occurs when two pieces of the crust move against each other, so the break between those pieces is by definition a fault. It might be a new fault, an active/recent fault or a previously inactive fault which has had some minor reactivation, but it's definitely a fault.

    Mining can cause collapses, but I wouldn't classify those as faults. It can also reactivate old faults, but really only enough to reduce the stress holding things together, so it's usually just minor remnants of stress that get released.


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    #25
    muckish
    Registered Users Posts: 610 ✭✭✭muckish


    HavingCrack wrote: »
    As a geography student I'm a tad embarressed asking this but I've never managed to get an answer I'm happy with :o.

    What causes earthquakes away from faultlines? I've heard mining, old plate boundaries etc. all put forward but I've never been satisifed.

    You need to realise the difference between a fault and a faultline. A fault being where rocks on one side slip passed rocks on the other side. A fault line is where a fault intersects the surface. So just because there's no faultline doesn't mean there's no fault. The fault could be large enough to cause a damaging earthquake but may still be too small to extend from the depths to the surface.
    So the earthquake could be due to other processes other than tectonic plate boundary movement, that build up pressure/stress and either release a deep fault or reactivate an old fault.


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    #26
    Judge
    Registered Users Posts: 507 ✭✭✭Judge


    This seems to be the best place to post this.

    Is Lough Tay in County Wicklow a Corrie Lake or a Ribbon Lake? Its position would suggest ribbon but the roughly circular shape and the great cliffs of Fancy mountain suggest corrie. Which is it?


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    #27
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭El Siglo


    Judge wrote: »
    This seems to be the best place to post this.

    Is Lough Tay in County Wicklow a Corrie Lake or a Ribbon Lake? Its position would suggest ribbon but the roughly circular shape and the great cliffs of Fancy mountain suggest corrie. Which is it?

    Lough Tay is a corrie lake or "cirque". Lough Dan on the other hand would be more likely to be a ribbon lake.


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    #28
    Judge
    Registered Users Posts: 507 ✭✭✭Judge


    El Siglo wrote: »
    Lough Tay is a corrie lake or "cirque". Lough Dan on the other hand would be more likely to be a ribbon lake.

    I thought it needed to be in a hanging valley to be a corrie though?


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    #29
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭El Siglo


    Judge wrote: »
    I thought it needed to be in a hanging valley to be a corrie though?

    No, you have to remember that the Wicklow mountains would have been bigger at one stage before but have weathered a fair bit hence the lack of a prominent hanging valley. It's still a corrie though, you can make out the headwall, the plucking zone and tarn from which the lake forms.


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    #30
    dogmatix
    Registered Users Posts: 1,404 ✭✭✭dogmatix


    El Siglo wrote: »
    Carlingford Lough and Lough Swilly are definitely fjords, this paper shows where the ice sheet carved out Carlingford Lough and this paper states Lough Swilly is fjord. So we definitely have three confirmed fjords in Ireland.

    Have not had time to read through the full paper (it's very technical and a bit above my level), but one of the diagrams in it shows glacial sea level higher the present sea level (figure 2). But I thought at the height of the last ice age sea levels where 100's of feet lower? Even accounting for the possibility that it might represent a time at an advanced state of warming and glacial melt (and the land rebounding after the weight of ice is removed above it), should not the glacial sea level be lower then present sea level?

    Forgive my geological ignorance but I am interested.

    Great thread by the way.


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    #31
    El Siglo
    Registered Users Posts: 3,803 ✭✭✭El Siglo


    dogmatix wrote: »
    Have not had time to read through the full paper (it's very technical and a bit above my level), but one of the diagrams in it shows glacial sea level higher the present sea level (figure 2). But I thought at the height of the last ice age sea levels where 100's of feet lower? Even accounting for the possibility that it might represent a time at an advanced state of warming and glacial melt (and the land rebounding after the weight of ice is removed above it), should not the glacial sea level be lower then present sea level?

    Forgive my geological ignorance but I am interested.

    Great thread by the way.

    Remember, glaciers are extremely heavy things (hint hint...;)). The sea-level we have now is a result of two things; glacial isostacy or isostatic rebound and eustacy (sea-level rise). Due to the weight of the ice (especially in the north of Ireland where one of the ice sheets advanced from) actually had enough weight to 'push down' as a manner of speaking the 'land level' (i.e. the actual physical mass of Ireland) hence sea-level appears higher but it's a result of isostacy and not eustacy (i.e. that sort of explains Fig 2). What happens and this is where it gets really confusing is which takes place faster or slower; isostacy or eustacy and in some cases they cancel each other out or we see drops or rises in sea-level. It gets a bit hairy and my explanation probably does it no justice, but I'm currently in the lab and my neck is killing me!:D

    Don't worry, I'm by no means not an expert on the subject! Glad you said "geological ignorance", some people don't even consider that kind of research to be geology, would you believe!:pac:


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