Uncrossable Marshes

[EddieH]

Further, as I said before, on Saturday I was neck deep and definitely not standing on anything hard - I'd simply reached my floating level.

I say this partly because it amuses me, but also to suggest that in a similar circmstance you'll be oay as long as you don't panic and drown through water in the lungs.

[mikey]

Horses now - they definitely disappear but I guess they are much denser than us

Well you rarely see any on University Challenge so I guess that must be the case.

[Red Adder]

[quote="mikey"][quote="EddieH"]Horses now - they definitely disappear but [b]I guess they are much denser than us[/b][/quote]

Well you rarely see any on University Challenge so I guess that must be the case.[/quote]


That's because that are not at university, and, unlike some Oxford students, realise that they are therefore not elligble

[King Penguin]

I'm still not convinced unless of course he has very dense stuff in his pack. As you say "still going down" - who's to stay he would not have stopped with his head out..

Even if he had, there's no way he would have got out unaided, and I certainly would not have liked to put it to the test. He was still going down even without his pack.

Horses now - they definitely disappear but I guess they are much denser than us, and no doubt panic as well.

Are they really ? I suspect most land-based mammals have a remarkably similar density, unless they are armour-clad like rhinos.
And humans wouldn't panic ?

[Copepod]

I suspect that the pressure exerted by part of body in contact with ground feet is more significant than the density of the whole body eg camels have wide pads to avoid sinking into sand, otters have webbed paws for swimming, but also to avoid sinking into mud, hoofed animals tend to exert relatively high pressure - and hence produce deep prints in mud or sand; seals are perhaps the least likely to sink into marsh or mud, as they rest on their bellies.

[geomorph]

Marsh/peat bog hydrology is extremely complex. It depends on many morphological and groundwater/drainage characteristics, and on the manner by which the vegetation developed overtime. The surface vegetation and indeed the various layers within the bog can infact contain significant portions of entrapped gases of decomposition eg methane. Materials in the bog can be held in various states of suspension and there can be less dense layers lying below denser layers. There can be free standing water at the base many metres deep, isolated by a mat of poorly decomposed vegatation supportingthe upper marsh/bog

EddieH is reasonably correct that most of the time the denisty of the marsh/bog is greater than that of the human and that it is struggling that in fact changes the dynamic (often by providing an exit route for entrapped gases and into which vacated volume the marsh/bog material moves and the person follows). Once this releasing starts the marsh can change rapidly from a fairly static feature in equilibrium to a rapidly re-configuring monster in which material separate out or mix together very fast.

Copepod correctly points out that the forces exerted by animals with 'large feet' are less than small footed. At the same time once the large foot breaks the resistance of the surface it is much harder to withdraw and animals such as horses have gaits that make it difficult to lift the legs out without increasing the rate of disturbance. Humans can adopt a breaststroke type approach and point hands and feet and thus 'float' in a single layer of the marsh/bog (unless you are unkucky enough to encounter the top layers with densities less than 1).


It is extremely difficult for a mapper to get the boundary between crossable/uncrossable correct for all times of the year. Indeed just to add to Mappingmum's comment - you may visit it after the storm from hell, but it is still crossable.... it becomes uncrossable at some time later because the lag time of the sources is non-linear. Think of them as pots filled to overflowing at different rates and for different reasons.

[EriOL]

To me it's simply bad coursesetting to create a leg where it's even possible that the fastest route cross an uncrossable feature. Routechoice problems sholdn't be based on chance!

[gg]

so we just have to cross them on our bellies?

[geomorph]

so we just have to cross them on our bellies?

Nah - just keep flying

[King Penguin]

To me it's simply bad coursesetting to create a leg where it's even possible that the fastest route cross an uncrossable feature. Routechoice problems sholdn't be based on chance!

Surely there is always an element of chance. The shorter rough open vs the longer path often depends on how runnable the rough open is, and you cannot know until you get there.

[Rich R]

Some who did the Jukola last year will have encoutered a man eating marsh within a steep sided valley shortly before the last control. This marsh was marked as crossable (somehow). When I crossed it I was pretty much at the ned of my 15km course and completely knackered. I could see I was going to get very wet and muddy as I ran down the bank but didn't expect to go up to my neck at the point I crossed! As I tried to pullmyself out my calf cramped up and all of a sudden I was in quite a dangerous situation and have to say I did panick a little. Fortunately the adreneline was enough to somehow drag myself out somehow after being in it for the best part of a minute.

If that marsh was crossable then the one in question was barely a puddle.