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Isostatic changes… Sea level changes… and a Rice Pudding.

bowl of rice pudding with a good skin on itThe planet Earth on which we stand, has a thin surface skin (lithosphere), which floats on top of a much thicker, semi-fluid, hot layer (asthenosphere).
A home made rice pudding with a skin comes in useful to visualise this and can be used to demonstrate a much larger, real Earth occurrence.
This real Earth occurrence is known as Isostatic Change, a vertical movement, both up and down, of the lithosphere. This can effect coastal communities by altering their sea levels.


The lithosphere on which we build, is flexible. It lays in equilibrium upon the asthenosphere until a vertical force effects it…. then the isostatic changes occur….. up until a new equilibrium is attained.


Cue the pud….
Get the permission of the pudding owner… then poke the pud. With the use of a finger, push vertically down, a little bit, on the skin and at that point it will sink down under the force, whilst somewhere else, the skin will lift up. Release your finger and the sunken point will slowly rebound, whilst the lifted area will sink back down.


Isostasy and isostatic change….
Isostasy is the cool word given to the skin of the pudding, or the lithosphere, when it is laying balanced, in equilibrium, on top of the semi-fluid below it, with no new vertcal forces acting on it.

Isostatic change, is what the poked pudding demonstrated. An isostatic change occurred as the pudding was being poked downwards. The skin was forced vertically, adjusting (downwards) to compensate, whilst elsewhere would rise in balance.


Sea level changes…. Back to the pud….
Poor a little milk into the valleys and let settle. Once all is settled (in its state of equilibrium), then use some imagination:

Imagine the pudding as a miniature Earth surface area, with islands surrounded by a sea. Imagine two communities on the ‘coastline’, then poke the pud again, near one of these communities.
The land, where poked, will sink below the surface…. to the occupants of that community, looking out:
* They would observe that their sea level was rising.
Elsewhere, if the second community was on a piece of land lifted up, then to the occupants of that community, looking out:
* They would observe that their sea level was dropping.


Real Earth occurrence….
No giant fingers have been spotted to date, but vertical forces such as massive tonnage of glaciers, force an isostatic change. The lithosphere below the glacier will sink down, whilst elsewhere there will be an uplift.
In the times when these glaciers melt away, that area will rebound back upwards whilst elsewhere will sink a little.

 montage of three images, land, land with sea, isostatic changes


An example of isostatic change occurring in this present day time….
The glaciers over Scandinavia are melting away and this area is rebounding. As a consequence of this, the land around the southwest of the UK is sinking.

It occurs too slowly for us to feel the land moving… It occurs in measurements, too small to notice on a daily observation, but over longer time frames…. it does occur. It can be measured in mm/year.


This is one of many Earth processes. Note that the sea level changes here are to do with the land moving vertically and not the sea increasing or decreasing in volume (another process)…. more later.


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8 Responses to "Isostatic changes… Sea level changes… and a Rice Pudding."

  1. admin says:

    Use the tabs under the post – ‘Previous Post’ ‘Following Post’ – First Post’ ‘Latest Post’ – to move along the stories of Prof Puckit… in order of writing.
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  2. Brenda P Jones says:

    Loved this. What a great way to describe, with interest, about one of our Earth processes.
    Also always good wholesome thing to promote rice-puddings!!!

  3. Dave says:

    Sink & BOING!!! very interesting method and idea to convey this process :o).

    True that it is not just water quantity that effects sea level changes, but the flexible earth surface also.

    Most helpful article.

  4. Elizabeth Aldrin says:

    This is a wonderful way of explaining this process. Very original style. I can use this to pass on this topic area of sea level change. This idea benfit Teaching/learning. Off to bake a rice pud as a prop.

  5. Catherine says:

    I can use this as an education story for Earth Science.
    I can use this also, in modern day typical discussions, regarding climate change and sea level change – but it will allow a greatly desired, very fresh angle, to be placed “in the mix”.

    Very helpful. Amusing and very fresh thinking. Thankyou

  6. Mike Palmer says:

    Class! Thanks. Can use this over and over for range of topics on near subject. It can be used on wide range of ages as well. Nicely thought of.
    Mike Palmer

  7. Bethany Harper says:

    Fascinating way of putting across this point. I’d heard of the Lithosphere, being the crusty area of our planet, so to understand it is “flexible”, and shifts up and down:
    🙂 as the rice pud skin 🙂
    is great way to visualise it. Will pass it on. Thankyou x

  8. Sam says:

    A rice pudding and planet earth? How do you come up with these notions. It fits so well and forces me to remember that the planet surface is indeed “soft” and somewhat flexible.
    Thanks for article. Put in a way that is most useable for education and interesting general interest.

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