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How are sandstone mountains formed?

Discussion in 'Geography' started by MelBrammer, May 11, 2017.

  1. MelBrammer

    MelBrammer New commenter

    Really hoping somebody can help me with some subject knowledge of geology here. I'm a Primary School Teacher. Our topic is Mountains, with a focus on the Black Mountains in South East Wales (where we're going on residential in a few weeks). Last week we learned about Block Mountains, Dome Mountains, Fold Mountains and Volcanic mountains, and a basic description of how they are formed. Next week we are looking at the Black Mountains in particular. On doing my homework I find that the Black Mountains are made of Old Red Sandstone from the late Silurian and early Carboniferous and that the hills and valleys were shaped by glaciers from north Wales (which makes U shaped valleys?). As you can tell, my Geog knowledge in this area is sadly lacking. I understood that sandstones were formed at the bottom of the ocean (like limestone)... so how do they end up being hills? Do they form sandstone first, and then one of my folding/block/dome processes lifts them up? Does the weight of all that ice on the northern part of the landmass lift this end up? Or does the sea level drop so dramatically? As you can see I am really not the right person to be teaching this series of lessons, but I'm hoping that I can work it out and stay slightly ahead of the class!
  2. tosh740

    tosh740 New commenter

    I think (and happy to be contradicted here) that the sediments formed on the sea bed are pushed up and folded by mountain building activity - so formed in the same way as fold mountains, such as the Andes, are today. These mountains are then weathered and eroded to look like they do today - glaciation being really significant. Layers of plasticine or even sugar paper pushed together and upwards would demonstrate this clearly.
    bonxie and Moony like this.
  3. Moony

    Moony Lead commenter

    Geography won't help you all the way with this as you are dealing with geology when you do mountain building properly.

    I'm not really sure where you are getting your terminology from to be honest. Here's a link that might help, tosh got the nub of it right but the link covers it in a lot more detail.


    Have a read of that and I'll happily handle questions you might have as best as I can.
    bonxie likes this.
  4. Flumptious

    Flumptious New commenter

    Sorry, this might be too late for you, but I am a geologist (who now wants to become a geography teacher). Tosh is right: the sandstone might have former in the sea or rivers (or importantly, in deserts - the Permo-Triassic New Red Sandstone formed in a desert. I have been to the Namib Desert, (which is, funnily enough, in Namibia!) a couple of times, once taking university students on a geology field-trip, so I have actually seen the dunes of sand, being blown around by the wind, which will one day form a sandstone, like the Permo-Triassic sandstone here in Britain).

    Anyway, the sand gets deposited, and then eventually it becomes sandstone. That sandstone gets buried by other sediments, normally over hundreds of millions of years. Then there is pressure, which fold the rocks, and force them up to form mountains. An awful lot of mountains now are made of rock that was formed on the seabed, hundreds of millions of years ago.
    Last edited by a moderator: May 25, 2017
    bonxie and tosh740 like this.

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