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The Physical Geography Thread

  • 27-05-2010 12:53am
    #1
    El Siglo
    Registered Users, Registered Users 2 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

  • #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 :)


  • #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:


  • #4
    El Siglo
    Registered Users, Registered Users 2 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:


  • #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?


  • #6
    El Siglo
    Registered Users, Registered Users 2 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?


  • #8
    El Siglo
    Registered Users, Registered Users 2 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


  • #9
    NotCarrotRidge
    Registered Users, Registered Users 2 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.


  • #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?


  • #11
    El Siglo
    Registered Users, Registered Users 2 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?


  • #13
    El Siglo
    Registered Users, Registered Users 2 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.


  • #14
    muckish
    Registered Users, Registered Users 2 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!


  • #15
    El Siglo
    Registered Users, Registered Users 2 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.


  • #16
    muckish
    Registered Users, Registered Users 2 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


  • #17
    El Siglo
    Registered Users, Registered Users 2 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!;)


  • #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


  • #19
    El Siglo
    Registered Users, Registered Users 2 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.


  • #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.


  • #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.


  • #23
    El Siglo
    Registered Users, Registered Users 2 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...


  • #24
    NotCarrotRidge
    Registered Users, Registered Users 2 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.


  • #25
    muckish
    Registered Users, Registered Users 2 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.


  • #26
    Judge
    Registered Users, Registered Users 2 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?


  • #27
    El Siglo
    Registered Users, Registered Users 2 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.


  • #28
    Judge
    Registered Users, Registered Users 2 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?


  • #29
    El Siglo
    Registered Users, Registered Users 2 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.


  • #30
    dogmatix
    Registered Users, Registered Users 2 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, Registered Users 2 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:


  • #32
    dogmatix
    Registered Users, Registered Users 2 Posts: 1,404 ✭✭✭dogmatix


    El Siglo wrote: »
    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:

    Thanks for the information El Siglo. Sounds very complicated - i'd hate to try and figure out the maths for isotacy vr's eustacy vr's glacial melt and all. I must get myself a good textbook on Geology.


  • #33
    angeldaisy
    Moderators, Education Moderators Posts: 2,282 Mod ✭✭✭✭angeldaisy


    Anyone help with out with a bit of clarification please?
    I've a geog exam tomorrow - 2nd yr 3rd level. I'm just a bit confused about the closure of the Iapetus ocean, do I have this right?

    It closed during the late silurian / early Devonian period; during the Ordovician period there was a period of volcanic activity and these formed island arcs in the Iapetus. it was the subduction of the ocean floor causing the island arcs to collide with the laurentia continent causing the caledonian orogeny.

    Does any of that make sense.... help please


  • #34
    NotCarrotRidge
    Registered Users, Registered Users 2 Posts: 160 ✭✭NotCarrotRidge


    angeldaisy wrote: »
    Anyone help with out with a bit of clarification please?
    I've a geog exam tomorrow - 2nd yr 3rd level. I'm just a bit confused about the closure of the Iapetus ocean, do I have this right?

    It closed during the late silurian / early Devonian period; during the Ordovician period there was a period of volcanic activity and these formed island arcs in the Iapetus. it was the subduction of the ocean floor causing the island arcs to collide with the laurentia continent causing the caledonian orogeny.

    Does any of that make sense.... help please

    Hi,

    You're pretty much spot on. The Ordovician volcanics only occur south of the Iapetus Suture, on what would have been Avalonia.

    The ocean closed (due to subduction) and Avalonia crashed into Laurentia, with the join being the Iapetus Suture. It runs from Limerick to Louth, approximately. The trend of the Caledonian Orogeny is parallel to that (SW-NE).

    Good luck.

    Iapetus_1.jpg


  • #35
    angeldaisy
    Moderators, Education Moderators Posts: 2,282 Mod ✭✭✭✭angeldaisy


    thank you so much for that, I think I'm working myself round in circles!


  • #36
    slowburner
    Moderators, Science, Health & Environment Moderators Posts: 5,221 Mod ✭✭✭✭slowburner


    I think I have learned the meaning of two new terms here isotacy and eustacy. Isotacy is the effect of the weight of ice pushing the land mass down and eustacy is the effect of rising sea levels?

    I need to get a rough idea what sea levels were like in Ireland between the first and fifth centuries AD. Were they higher or lower than today, if so then roughly by how much?
    Thanks.


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  • #37
    NotCarrotRidge
    Registered Users, Registered Users 2 Posts: 160 ✭✭NotCarrotRidge


    slowburner wrote: »
    I think I have learned the meaning of two new terms here isotacy and eustacy. Isotacy is the effect of the weight of ice pushing the land mass down and eustacy is the effect of rising sea levels?

    I need to get a rough idea what sea levels were like in Ireland between the first and fifth centuries AD. Were they higher or lower than today, if so then roughly by how much?
    Thanks.

    You kind of have it. Isostasy is just the reaction of the land mass to extra weight, so it can be upwards or downwards. It happens slowly, which is why most of Northern Europe is still on the way back up since the end of the last ice age.

    Sea levels between 1st and 5th centuries would have been much the same as they are now. There was a warming period later than that, but it's not as if it would have had any kind of significant impact on sea level. I don't have any figures for this, but I really don't think there can have been an appreciable difference between then and now.


  • #38
    NotCarrotRidge
    Registered Users, Registered Users 2 Posts: 160 ✭✭NotCarrotRidge


    angeldaisy wrote: »
    thank you so much for that, I think I'm working myself round in circles!

    You're welcome. How did it go?


  • #39
    El Siglo
    Registered Users, Registered Users 2 Posts: 3,803 ✭✭✭El Siglo


    NotCarrotRidge wrote: »
    You kind of have it. Isostasy is just the reaction of the land mass to extra weight, so it can be upwards or downwards. It happens slowly, which is why most of Northern Europe is still on the way back up since the end of the last ice age.

    Sea levels between 1st and 5th centuries would have been much the same as they are now. There was a warming period later than that, but it's not as if it would have had any kind of significant impact on sea level. I don't have any figures for this, but I really don't think there can have been an appreciable difference between then and now.

    That's a very contentious point and I've had many arguments over that one. There's evidence that sea-level was reasonably lower than present, definitely in the north coast areas where you see the greatest isostacy taking place (where the rise in sea-level is negated by the fact that isostacy is of a much greater magnitude between 1.3 - 3 mm per annum). I wouldn't say that sea-level was terribly lower than present (not like the LGM), but I wouldn't be inclined to say that the 1st to 5th century and now are the same.

    Sorry if I sound like a bit of a dick, I don't mean to be at all.


  • #40
    NotCarrotRidge
    Registered Users, Registered Users 2 Posts: 160 ✭✭NotCarrotRidge


    El Siglo wrote: »
    That's a very contentious point and I've had many arguments over that one. There's evidence that sea-level was reasonably lower than present, definitely in the north coast areas where you see the greatest isostacy taking place (where the rise in sea-level is negated by the fact that isostacy is of a much greater magnitude between 1.3 - 3 mm per annum). I wouldn't say that sea-level was terribly lower than present (not like the LGM), but I wouldn't be inclined to say that the 1st to 5th century and now are the same.

    Sorry if I sound like a bit of a dick, I don't mean to be at all.

    No, you're not being a dick. I don't disagree that it was probably a bit lower, I suppose my point was that for the purposes of the question asked, it probably wouldn't have made much difference at all.


  • #41
    slowburner
    Moderators, Science, Health & Environment Moderators Posts: 5,221 Mod ✭✭✭✭slowburner


    El Siglo wrote: »
    That's a very contentious point and I've had many arguments over that one. There's evidence that sea-level was reasonably lower than present, definitely in the north coast areas where you see the greatest isostacy taking place (where the rise in sea-level is negated by the fact that isostacy is of a much greater magnitude between 1.3 - 3 mm per annum). I wouldn't say that sea-level was terribly lower than present (not like the LGM), but I wouldn't be inclined to say that the 1st to 5th century and now are the same.

    Sorry if I sound like a bit of a dick, I don't mean to be at all.
    You raise my hopes and dash them all in the one breath.
    I had been expecting/hoping that sea levels might have been higher during this period.
    If they had been higher, a particular river I am interested in might have been navigable further upstream - this would have been exciting news.
    Ah well.


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  • #42
    El Siglo
    Registered Users, Registered Users 2 Posts: 3,803 ✭✭✭El Siglo


    NotCarrotRidge wrote:
    No, you're not being a dick. I don't disagree that it was probably a bit lower, I suppose my point was that for the purposes of the question asked, it probably wouldn't have made much difference at all.

    No worries, I know what you mean now! :pac:
    slowburner wrote: »
    You raise my hopes and dash them all in the one breath.
    I had been expecting/hoping that sea levels might have been higher during this period.
    If they had been higher, a particular river I am interested in might have been navigable further upstream - this would have been exciting news.
    Ah well.

    Well actually who's to say that the river wasn't navigable upstream? If you're looking at the medieval warm period then it is quite possible because we would have had more rain (i.e. more energy means that clouds would be able to hold more water and then release more water) which may mean that there may have been raised water levels within rivers and possible larger water discharge. So if you have more water say within the fluvial system then there could have been deeper water further upstream. Also, the land level (depending on whether it's down south or north) may have been lower if it was down south, so there still might be a possibility for the situation that you're looking at. It's just a hypothesis, I could be completely wrong, you may go out and test for it. If I were you I'd speak to Robin Edwards (sea-level expert) in TCD and Conor Murphy in NUIM (he's a hydrologist, knows his stuff).


  • #43
    NotCarrotRidge
    Registered Users, Registered Users 2 Posts: 160 ✭✭NotCarrotRidge


    slowburner wrote: »
    You raise my hopes and dash them all in the one breath.
    I had been expecting/hoping that sea levels might have been higher during this period.
    If they had been higher, a particular river I am interested in might have been navigable further upstream - this would have been exciting news.
    Ah well.

    Unlucky, sb.


  • #44
    slowburner
    Moderators, Science, Health & Environment Moderators Posts: 5,221 Mod ✭✭✭✭slowburner


    El Siglo wrote: »

    Well actually who's to say that the river wasn't navigable upstream? If you're looking at the medieval warm period then it is quite possible because we would have had more rain (i.e. more energy means that clouds would be able to hold more water and then release more water) which may mean that there may have been raised water levels within rivers and possible larger water discharge. So if you have more water say within the fluvial system then there could have been deeper water further upstream. Also, the land level (depending on whether it's down south or north) may have been lower if it was down south, so there still might be a possibility for the situation that you're looking at. It's just a hypothesis, I could be completely wrong, you may go out and test for it. If I were you I'd speak to Robin Edwards (sea-level expert) in TCD and Conor Murphy in NUIM (he's a hydrologist, knows his stuff).
    Thanks very much for the contacts El Siglo. Much appreciated. I'll send an email or two, one of these days.

    The river in question is the Avoca in Wicklow. It is very much a spate river, subject to rapid rises and falls in water levels. The descent of the river is precipitous in places.
    In high water, it is a raging torrent and in low water, it is far too shallow for the passage of most boats - you could easily cross the shallows in your wellies.

    Whether or not the topography made for a river of a different character in the late iron age/early medieval, is another question.
    The brute force of some of its floods are astonishing. I have witnessed maybe four or five significant floods on this river in recent years; each one had the capacity to alter the river's topography - add those together over a thousand or so years and there could indeed have been quite a bit of change to the structure of the river.

    That said, I suspect that the only likelihood of it being navigable further upstream than today, would be if higher tides caused freshwater to back up and become deep and 'slack' - if you know what I mean. Today the river is tidal for perhaps a couple of kilometres or so above the mouth at Arklow. I heard mention somewhere that it was tidal to a point some 8 - 10 km up to Woodenbridge - but I am unsure what period this was.


  • #45
    owenc
    Banned (with Prison Access) Posts: 5,524 ✭✭✭owenc


    I was just reading this. I seen about the laurentian plate. I know that we and scotland were apart of it. Does that mean that the rock here is the same type found in north america for example the canadian shield and what caused us to break off anyway. Surely we can't just break off a plate can we?


  • #46
    NotCarrotRidge
    Registered Users, Registered Users 2 Posts: 160 ✭✭NotCarrotRidge


    owenc wrote: »
    I was just reading this. I seen about the laurentian plate. I know that we and scotland were apart of it. Does that mean that the rock here is the same type found in north america for example the canadian shield and what caused us to break off anyway. Surely we can't just break off a plate can we?

    Yes, there are some very similar rocks between here and Newfoundland for example.

    Plates have changed, disappeared and grown throughout Earth's history. For example, at the moment, the Juan de Fuca plate is being subducted under the North American Plate, and it was part of a much bigger plate, most of which is now gone.


  • #47
    Scrappychimow
    Closed Accounts Posts: 1,040 ✭✭✭Scrappychimow


    Ok,
    Lest finish the year with a tasty question, hopefully someone can provide an even tastier answer...

    Please tell me how Sea level rise from the Holocene is responsible for the formation of barrier island lagoons in South east Ireland.

    I know the barriers are sorted glacial deposits and that the lagoon is on the backside of them (not seawards).
    But how is sealevel linked to their formation?


  • #48
    CajunOnTour
    Banned (with Prison Access) Posts: 82 ✭✭CajunOnTour


    Eh...the sea flooded the land between them and the coast? ;)


  • #49
    Scrappychimow
    Closed Accounts Posts: 1,040 ✭✭✭Scrappychimow


    CajunOnTour wrote: »
    Eh...the sea flooded the land between them and the coast? ;)

    Woww!!!!! What an intelligent reply , you really know what you're talking about don't you?


  • #50
    El Siglo
    Registered Users, Registered Users 2 Posts: 3,803 ✭✭✭El Siglo


    Scrappychimow wrote: »
    Ok,
    Lest finish the year with a tasty question, hopefully someone can provide an even tastier answer...

    Please tell me how Sea level rise from the Holocene is responsible for the formation of barrier island lagoons in South east Ireland.

    I know the barriers are sorted glacial deposits and that the lagoon is on the backside of them (not seawards).
    But how is sealevel linked to their formation?

    I went through a thesis there from an American chap, and he has given probably one of the more understandable explanations regarding your question:
    Transgressive shorelines along the Atlantic coast of North America [still very applicable to Ireland] are dominantly influenced by relative sea level rise and a low contribution of sediments from rivers and streams draining into the area (Kraft, 1978). The balance between wave energies, tidal ranges and prisms, erosion rates, and antecedent topography are the driving forces in barrier island morphology and migration (Dalrymple et al., 1992; Harris et al., 2002). Under these conditions, if sea level rise and erosion rates are balanced, barriers may migrate more or less continuously landward as sea level rises. Any back barrier lagoonal facies would likely be eroded in this process (Reinson, 1992). Alternatively, if the rate of sea level rise exceeds erosion rates, barriers may remain in place as sea level rises to the level of the top of the dunes; then the surf zone may “jump” landward to establish a new shoreline, thus drowning the barrier in place (Sanders and Kumar, 1975). In this case, an entire sequence of transgressional lagoon facies may be preserved (Reinson, 1992).

    You might want to read on some of the stuff by JAG Carter in UU, J. Orford in QUB etc... They're experts on gravel barriers and will probably have a few articles in Marine Geology and Zeitschrift für Geomorphologie.


  • #51
    Scrappychimow
    Closed Accounts Posts: 1,040 ✭✭✭Scrappychimow


    El Siglo wrote: »
    I went through a thesis there from an American chap, and he has given probably one of the more understandable explanations regarding your question:


    You might want to read on some of the stuff by JAG Carter in UU, J. Orford in QUB etc... They're experts on gravel barriers and will probably have a few articles in Marine Geology and Zeitschrift für Geomorphologie.

    Cheers that gives me a better idea , will look them up .


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