Continental Drift

[+BigFurryMonster]

http://en.wikipedia.org/wiki/Continental_drift

 

Continental Drift means that the earth in constantly moving. Plate tectonics make landmasses move along the surface of the earth. The rate at which this happens can vary up to 17 cm/year! North America is currently slowly drifting to the west at a rate of about 1.5 cm/year.

 

How will this affect the GPS system over the years? I can imagine that significant gaps between the calculated and actual position begin to appear over time. This leads to the question: when was the coordinate system initiated? Is it 'updated' somehow?

 

Interesting stuff.

[+JohnnyVegas]

I will not effect your GPS accuracy, the best you are going to get with any consumer grdae GPS is 3 meters in accuracy so 17cm is not really anything to sorry about.

[+AtoZ]

The actual location NEVER change just the location of the object. Say you have a benchmark at lat 30.00000 long 90.0000 well in say 5 year with a drift of 15 cm per year you might now have a location of 30.0001 90.0001, okay it is just an rought example but you get the idea I hope. The concept of Lat/Long is just a construct that is NOT depend upon what under lies i.e. land masses. So bassically NO contential drift will NOT affect the GPS. But it will affect the location of your cache, LOL.

cheers

[+WizCreations]

it would take almost 36 years for a cache to move 20 ft (approximately 609 cm) from the listed coordinates, and by that time, I would suspect that any cache would have been archived, moved, etc.

[+edscott]

Yes it has been updated, but more because of better data than drift. ....1929 then 1984 at least. Also the magnetic poles are drifting.. So many things to worry about. I think I'll just go out in the woods and try to sort it all out.... maybe catch a cache as it drifts by. []

[+WizCreations]

maybe catch a cache as it drifts by. []

you'd drift by too

[+edscott]

NO... you sit on the edge of a plate...

[+RJFerret]

it would take almost 36 years for a cache to move 20 ft...

 

Now THAT explains why those caches placed in 2002 always seem to be about 2' off!!!

 

LOL,

 

Randy

[+Gecko1]

I would assume that the satelites would have been updated by then.

[+tozainamboku]

Longitude is measured realative to Greenwich, England. Latitude is measured relative to the equator. As the tectonic plates move relative to one another and relative to the equator, Latitude and Longitude of a place fixed to a plate does change. Geocaches on the other hand, drift from their original position as finders rehide them. For most geocaches, this drift will be far bigger than the continental drift. Given the accuracy and precision of GPS you can expect at least 3 meter error in the posted coordinates, so continental drift won't affect hunting for caches. I can however vouch that finder drift has caused geocaches to move a significant distance.

[dsandbro]

it would take almost 36 years for a cache to move 20 ft (approximately 609 cm) from the listed coordinates, and by that time, I would suspect that any cache would have been archived, moved, etc.

So in 72 years the error could be 40 feet.

 

Everyone: report back here in 72 years (July 26, 2077) and tell us if you had any problems finding a cache because the coordinates were off.

[+reveritt]

I imagine that this very small correction would be taken care of by WAAS, which supplies correction data based on the difference between known locations of earth stations, and their apparent locations as indicated by GPS.

[+AtoZ]

Longitude is measured realative to Greenwich, England. Latitude is measured relative to the equator. As the tectonic plates move relative to one another and relative to the equator, Latitude and Longitude of a place fixed to a plate does change. Geocaches on the other hand, drift from their original position as finders rehide them. For most geocaches, this drift will be far bigger than the continental drift. Given the accuracy and precision of GPS you can expect at least 3 meter error in the posted coordinates, so continental drift won't affect hunting for caches. I can however vouch that finder drift has caused geocaches to move a significant distance.

The Equator will NEVER change and I think that only Greenwich was an old referance point not an absolute. So you will NEVER have a change in the Latitude. The Longitude I'll have to check I know historically that zero longitude has changed depending up on the current ruling naval power. It was not till 1884 that it was set in Greenwich as the standerd. But this is only a construct it is not abosulte and can remain the same even if England moved a 100 miles east. It is not absolute but a referance system based upon man drawing a grid system around the world. You could redefine the Prime Maridian as being New York, or even Las Angelas. It would really depend upon what new standard we established. But the plats moving under is imiganary grid will not affect the GPS accuracy.

cheers

[+fizzymagic]

I imagine that this very small correction would be taken care of by WAAS, which supplies correction data based on the difference between known locations of earth stations, and their apparent locations as indicated by GPS.

WAAS is not intended to correct for continental drift. The WAAS corrections don't work that way. However, they probably do provide some correction indirectly. I would imagine that the positions of the WAAS ground stations have to be updated every few years as the ground stations move, especially in California, where a good earthquake can move the whole plate a couple of feet in less than a minute!

 

Your GPS measures its latitude and longitude relative to the WGS-84 coordinate system. Continental drift will show up as a change in the latitude and longitude of a given spot on a continent. Over a time span of decades, it may even be detectable.

 

Correcting the cache coordinates to account for continental drift is the cache owner's responsibility, since, technically, the cache is moving.

 

Actually, now that I think on it, we should ban all caches, since they are all moving caches!

[+sbell111]

The above posters are correct in that continental drift will likely never be a real factor in this game. However, it seems to me that any land movement will result in the location moving away from the previously computed coords. Obviously, this movement tends to be tiny enough to be ignored over the short- and mid-term.

 

Latitude is an interesting topic in itself. I tried to find how the equator was determined and the best I did was locate a definition which stated that it was an imaginary line drawn around the planet, halfway between the poles. I suppose that the true equator would wander with any shifts in the earth's poles. If the equator, for plotting purposes, was adjusted with the shift of the poles, latitude would change. In practice, I'm sure that no adjustment is ever made.

[+tozainamboku]

The earth spins on its axis. Where the axis intersects the surface of the earth are the true north and south poles. The magnetic north and south poles wander relative to the true north and south poles due to various reasons. The magnetic poles have no effect on latitude or longitude. The equator is defined by where a plane perpendicular to the axis and halfway between the north and south poles intersects the surface of the earth. WGS84 latitude is define as the angle a line perpendicular to the surface of the earth makes with the equator. Longitude is the angular measurement between a point on the surface of the earth and another point at the same latitude on the prime meridian. The prime meridian is a line on the surface of the earth from the true north pole to the true south pole that passes through a specific point in Greenwich.

 

As the tectonic plates move, the Latitude and Longitude of a point fixed to a plate will change.

Edited July 26, 2005 by tozainamboku

[+sbell111]

The planet doesn't spin around the axis created by the magnetic poles? Huh. You learn something new every day.

[whiskeylover]

No, the earth spins around its true poles. Which are different from the magnetic poles.

[+AtoZ]

The earth spins on its axis. Where the axis intersects the surface of the earth are the true north and south poles. The magnetic north and south poles wander relative to the true north and south poles due to various reasons. The magnetic poles have no effect on latitude or longitude. The equator is defined by where a plane perpendicular to the axis and halfway between the north and south poles intersects the surface of the earth. WGS84 latitude is define as the angle a line perpendicular to the surface of the earth makes with the equator. Longitude is the angular measurement between a point on the surface of the earth and another point at the same latitude on the prime meridian. The prime meridian is a line on the surface of the earth from the true north pole to the true south pole that passes through a specific point in Greenwich.

 

As the tectonic plates move, the Latitude and Longitude of a point fixed to a plate will change.

By your Own defination the equator WILL NOT change as it is the half way point betwwwn the NORTH and SOUTH poles. The PRIME MARIDIAN is not a fixed point either but an arbertray assigned one.

cheers

[+edscott]

it would take almost 36 years for a cache to move 20 ft...

 

Now THAT explains why those caches placed in 2002 always seem to be about 2' off!!!

 

LOL,

 

Randy

Well it certainly explains why none drifted by this afternoon...

[+Isonzo Karst]

STOP Plate Techtonics!

[+Wacka]

Besides the magnetic pole drifting (it left Canada a few weks ago), the poles will flip. This has happened numerous times and its cause is not entirely clear. Some scientists think it is due to eddies in the molten iron outer core.

[+reveritt]

The earth spins on its axis. Where the axis intersects the surface of the earth are the true north and south poles. The magnetic north and south poles wander relative to the true north and south poles due to various reasons. The magnetic poles have no effect on latitude or longitude. The equator is defined by where a plane perpendicular to the axis and halfway between the north and south poles intersects the surface of the earth. WGS84 latitude is define as the angle a line perpendicular to the surface of the earth makes with the equator. Longitude is the angular measurement between a point on the surface of the earth and another point at the same latitude on the prime meridian. The prime meridian is a line on the surface of the earth from the true north pole to the true south pole that passes through a specific point in Greenwich.

 

As the tectonic plates move, the Latitude and Longitude of a point fixed to a plate will change.

By your Own defination the equator WILL NOT change as it is the half way point betwwwn the NORTH and SOUTH poles. The PRIME MARIDIAN is not a fixed point either but an arbertray assigned one.

cheers

Yes, but the equator is not a point fixed on one of the earth's tectonic plates. A cache hiding place is. If North America is drifting with respect to the global datum (WGS84) then the actual coordinates of caches are drifting with it. However, the rate of displacement is so slow that it makes no practical difference for geocaching.

[+AtoZ]

The earth spins on its axis. Where the axis intersects the surface of the earth are the true north and south poles. The magnetic north and south poles wander relative to the true north and south poles due to various reasons. The magnetic poles have no effect on latitude or longitude. The equator is defined by where a plane perpendicular to the axis and halfway between the north and south poles intersects the surface of the earth. WGS84 latitude is define as the angle a line perpendicular to the surface of the earth makes with the equator. Longitude is the angular measurement between a point on the surface of the earth and another point at the same latitude on the prime meridian. The prime meridian is a line on the surface of the earth from the true north pole to the true south pole that passes through a specific point in Greenwich.

 

As the tectonic plates move, the Latitude and Longitude of a point fixed to a plate will change.

By your Own defination the equator WILL NOT change as it is the half way point betwwwn the NORTH and SOUTH poles. The PRIME MARIDIAN is not a fixed point either but an arbertray assigned one.

cheers

Yes, but the equator is not a point fixed on one of the earth's tectonic plates. A cache hiding place is. If North America is drifting with respect to the global datum (WGS84) then the actual coordinates of caches are drifting with it. However, the rate of displacement is so slow that it makes no practical difference for geocaching.

But this has NOTHING to do with accuracery of your GPSr. Yes the cache will move but that only effects the location of the cache not the GPS coordinates system. And the Poles reversing is the MAGNETIC poles NOT the axial poles on which the earth spin. The euator will always be in the same spot.

cheers

[+BigFurryMonster]

OK - so the WGS84 Datum System will not be affected, but the earth and all caches on it may drift 'under' this system...

 

About the location of the equator:

 

The text at the Fake Equator Cache in Ecuador states that 'due to annual planetary variations the equator is now located north of the yellow line' ...

 

(the location of the yellow line having been determined between 1736 and 1744)

 

What's up with that?

Edited July 27, 2005 by BigFurryMonster

[+reveritt]

...

 

What's up with that?

The Earth's axis of rotation is subject to a number of periodic variations, which is one reason we need a new datum from time to time. When the axis moves a bit, the equator moves with it.

[+geoaware]

Wow...now this is starting to sound like great Earthcache material.....

[+TeamRJJO]

The Earth's axis of rotation is subject to a number of periodic variations, which is one reason we need a new datum from time to time.  When the axis moves a bit, the equator moves with it.

The two are really not related.

 

The motion of the Earth's axis has two parts -- precession and nutation. Precession is the motion of the axis in a large circle over a roughly 26,000 year period. Nutation is a harmonic with a roughly 18.6-year period, superimposed on top of the precession circle.

 

Although the axis moves, the equator always remains fixed with respect to the axis. The equator does move with respect to the ecliptic, but since GPS coordinates are referenced to an Earth-centered, Earth-fixed plane, this movement of the equator with respect to the Earth-Sun line is transparent to GPS.

 

NGA issues a new map datum every 5-7 years. This is simply a function of measurements being refined enough to warrant the issue of a new datum. It's not tied to any natural event.

 

Peace,

TeamRJJO

Edited July 28, 2005 by TeamRJJO

[+Deneye]

One thing not yet mentioned has been one of the islands that was affected by the earthquake which caused the december tsunami west of Thailand...Sumatra I believe. The whole island is apparently 100 feet south of where it once was.

 

To me that's a signifcant shift which would put any cache in jeopardy...

 

mind you..I only ever heard this reported once throughout the whole month or so afterwards and never again by any other news agency so maybe it just wasn't true..

 

The point being, who cares about continental drift, it's the earthquake that'll get us in the end.

[+BigFurryMonster]

In the Sumatra case, the tsunami would have destroyed all caches in the area. This cache in Thailand is an example.

 

I don't believe the entire island is as much as 33 meters (100 feet) off, really. But some movement could have happened.

[+BigFurryMonster]

Ah -- here we have it:

 

http://www.boston.com/news/world/asia/arti...shortened_days/

 

"We know we have movements of over a meter (yard), perhaps a couple of meters," said Ken Hudnut, a California-based geophysicist with the U.S. Geological Survey. "But the idea that Sumatra has moved 100 feet is just wrong."

 

(I hope this guy knows the difference between a yard and a meter)

 

Scientists at NASA, the U.S. space agency, said the Dec. 26 quake -- the largest to rattle Earth since 1964 in Alaska -- disrupted the planet's rotation and shaved 2.68 microseconds, or millionths of a second, from the length of a day.

 

NASA scientists B. F. Chao and Richard Gross calculated it shifted Earth's mean north pole about 1 inch and made the planet slightly less oblate, or flattened at the poles.

Edited July 28, 2005 by BigFurryMonster

[+AtoZ]

That is well and good bigfurry and valid but what your talking about does NOT have anything to do with plate tectonics it has to do with actually changes in the earths structire as the article states. But in the long run doe it matter the GPS is NOT that accurate any ways. So lets just put our plates away.

cheers

[+Deneye]

That is well and good bigfurry and valid but what your talking about does NOT have anything to do with plate tectonics it has to do with actually changes in the earths structire as the article states.

I beg to differ seeing as how earthquakes are caused by plate tectonics & continental drift.

 

Thanks BFM...that was the info I was talking about.

 

Ok..so I was off by 99 meters (somedays that is a regular occurrance)

[+BigFurryMonster]

Ok..so I was off by 99 meters (somedays that is a regular occurrance)

That's not good for finding caches!!

[+AtoZ]

That is well and good bigfurry and valid but what your talking about does NOT have anything to do with plate tectonics it has to do with actually changes in the earths structire as the article states.

I beg to differ seeing as how earthquakes are caused by plate tectonics & continental drift.

 

Thanks BFM...that was the info I was talking about.

 

Ok..so I was off by 99 meters (somedays that is a regular occurrance)

True but the OP was refering to normal plate drift.

cheers

[+TerryDad2]

I suppose to confuse things even further, the earth is not a perfect sphere. I've seen it described as a squished bumpy pear. (And no that is not a technical description you'll find in the scientific literature )

[+TeamRJJO]

I suppose to confuse things even further, the earth is not a perfect sphere. I've seen it described as a squished bumpy pear. (And no that is not a technical description you'll find in the scientific literature )

I think "oblate spheroid" is the approved industry term for "squished bumpy pear."