Tuesday, January 8, 2019

1/8/19 Report - How Mammoths Were Killed by Man. Water Forces and How Objects Move on a Beach.

Written by the TreasureGuide for the exclusive use of treasurebeachesreport.blogspot.com.

A flint point was found in a mammoth bone that provides clues about how mammoths were killed.  Here is an excerpt from that report.

"Among tens of thousands of bones, during a detailed analysis of the remains, I came across a damaged mammoth rib. It turned out that a fragment of a flint arrowhead was stuck in it. This is the first such find from the Ice Age in Europe!" - told PAP Dr. Piotr Wojtal from the Institute of Systematics and Evolution of Animals PAS in Kraków. The analyses, co-financed with the National Science Centre grants, are conducted jointly with Dr. Jarosław Wilczyński.

Wojtal reminds that the scientific community has been discussing for years how our ancestors killed mammoths. According to some researchers, these animals were killed by trickery - chasing them to the pits or towards bluffs, from which they would fall. Others say that people focused on weaker or sick animals. Some think that mammoths were hunted...

Here is the link for more about that.



On different occasions I've talked about how coins and items move on a beach and the forces that move them.  Today I'll address the complexity of the water forces.

There are many different water forces that act on an item on a beach.  First of all, the water doesn't hit the beach or an individual item from just one direction.  The most obvious example is the incoming and outgoing water after each wave.  The incoming water hits in one direction, and the outgoing water, if it gets there, from another direction.  But there will often be a primary and secondary swell too, and they will hit the beach from different angles.

Not only can the water come from almost any direction, but the amount of force will vary dramatically too. The amount of force can be nearly zero or very violent.  The force of a crashing wave can be great.  That is water crashing down.  A breaking wave can also, or a passing wave can also lift sand and other items.  I've shown pictures of that before.

Considering all that, an item can be hit from almost any direction and with greatly varying amount of force, but that is not all.  The force will also be different on different parts of a single object.

I once posted a link to a video showing an experiment in which a stream of water was directed up a sandy slope and over an object that was sitting on the slope in shallow water.  The amount of force was sufficient to move the sand on the front of the object, but not enough to push the object up the slope.  The result was that the object slipped down the sandy slope in steps.  When enough sand was moved from the down-slope side of the object, the object slipped down and settled again until enough sand was moved so the object slipped down again.  As the water flowed around the object, the sand on one side (the down-slope side) was moved away until gravity moved it down the slope.

I described that experiment in more detail in a March 2014 post.  Here is the illustration and brief description of the experiment.

Object On Sandy Slope and Stream or Current Directed Up Hill.

The current pushed the sand away from the front and sides of the object as the water rushed around it.  The object then STEPPED down the slope.  I say "stepped" because it moved in small quick steps, pausing in between steps.

The current moved the sand from the front of the object but not the back of the object.  Gravity on the object and also the sand behind the object then moved the object down the slope.

The current trigger or threshold level was sufficient to move the sand in the current up the slope but gravity moved the object down the slope.

Here is the link to that post, which also described another related experiment.


It might seem surprising that the object actually moved opposite the current, but that is the way it worked out.

If this was a wave, instead of a steady stream, you'd also have returning water too instead of water running in one direction, and that could move sand down the hill faster than the object moved down the hill.  And that could bury the object.

You have vastly different amounts of force at different times and locations.  The amount of force of a crashing wave can throw objects and suspend a lot of sand.

I think you can see how complex this is with the water moving  in a variety of different directions and with varying amounts of force.

How an object moves on a beach depends on how the water moves the sand in relation to other objects.  Different objects require different amounts of force to be moved.  The sand moves easier and faster and uncovers or covers objects that move at a different rate.

I've discussed that before along with the subject of thresholds and trigger rates.


Not much surf this week.

Predicted Surf.
Source: MagicSeaWeed.com
Happy hunting,