Changing airport elevations

[amillet]

When I learned to fly in 1989 our airport elevation was 144 feet.  Nearby Port Angeles was 288 feet.  Easy to remember. (2 x 144=288).  Yesterday while doing some approaches my safety pilot mentioned airport elevation was 291.  I have no idea when the reported elevation changed. Just checked my home airport (W28-Sequim, WA). It too has changed to 151 feet.  Is it continental drift/uplift?  More accurate measurements?

[N201MKTurbo]

I thought all this carbon dioxide from aviation was making the oceans rise.

I'm so confused.......

[carusoam]

Expect that it is accuracy of measurement and recording...

There can be some change...

my home port had a magnetic shift... Runway 27 became rwy 28 after several decades.

Best regards,

-a-

[lamont337]

Depends on where the measurement is taken on the field as well. Port Angeles elevation is listed as 291 but the Touch Down Zone Elevation listed for the ILS 8 is 284.

[kortopates]

I asked my wife, la profesora de Geofísica, and she said it could be any of those things. But I'd blame it on the Olympic mountains  but it would take some reading to really find out.

[kortopates]

12 minutes ago, lamont337 said:

Depends on where the measurement is taken on the field as well. Port Angeles elevation is listed as 291 but the Touch Down Zone Elevation listed for the ILS 8 is 284.

Interesting thought. Of course the airport elevation is based on the geometric center of the airport and since the airport is on a pretty good gradient there is a 44' difference between the threshold elevations of 13 and 31. But unless the airport configuration was changed  in the last 30 years the geometric center hasn't changed either. But all it would take would be lengthening of a runway or if both runways didn't exist back then. 

[Bob - S50]

From the AIM: AIRPORT ELEVATION− The highest point of an airport’s usable runways measured in feet from mean
sea level.

So if there was a runway that runs uphill and it gets extended further up the hill, the airport elevation should change too.  The guess about the area being lifted as the Olympics continue to rise sounds reasonable to me though.

I've been known to make a few landings that reduce the field elevation.

[Hank]

2 hours ago, Bob - S50 said:

The guess about the area being lifted as the Olympics continue to rise sounds reasonable to me though.

The Olympics may still be rising, but that's generally tiny fractions of an inch per decade. Several feet would require large-scale earthquakes.

I'd go for either land acquisition or runway extensions.

[EricJ]

One of the ways that they monitor the 'progress' of the Yellowstone caldera is how much the ground swells or recedes.   There's a lake that the relative depths at the two ends have changed substantially because the swell is greater at one end than the other.

Depletion of groundwater or extraction of other underground resources can cause sinking as well.

It seems like there are a lot of things that can affect this, so who knows.

Way back when I was first learning to fly before things like ATIS existed (and at an untowered field), it was normal to just set the altimeter to field elevation.   Later when local pressure was more easily available it was a bit of an eye opener to see how much difference there typically was between the field elevation and what the altimeter said when set to local pressure.    I don't think I ever considered an altimeter a precision instrument after that.   I like that GPS provides another useful data point.

[amillet]

2 hours ago, Hank said:

The Olympics may still be rising, but that's generally tiny fractions of an inch per decade. Several feet would require large-scale earthquakes.

I'd go for either land acquisition or runway extensions.

Neither of those have occurred.

[ShuRugal]

Mean Sea Level is also subject to change, because MSL is an idealized fiction.

[air cooled dad]

I was happy when the elevation at KORD changed from 666’.  

 

Jason

[Pissed'Ole-Pete]

7 hours ago, ShuRugal said:

Mean Sea Level is also subject to change, because MSL is an idealized fiction.

But if Sea level is rising... shouldn't field elevation drop?

[ShuRugal]

But if Sea level is rising... shouldn't field elevation drop?

Now that is an interesting question. Because of the way MSL is calculated, and all the other factors which impact the actual height of the cost lines, the volume of water in the seas can increase, while MSL falls.

MSL really is a purely fictitious construct, because the conditions it assumes (all water on Earth in a resting state with no external forces aside from gravity acting on it) can never exist.

Sent from my Pixel using Tapatalk

[Pissed'Ole-Pete]

4 minutes ago, ShuRugal said:

Now that is an interesting question. Because of the way MSL is calculated, and all the other factors which impact the actual height of the cost lines, the volume of water in the seas can increase, while MSL falls.

MSL really is a purely fictitious construct, because the conditions it assumes (all water on Earth in a resting state with no external forces aside from gravity acting on it) can never exist.

Sent from my Pixel using Tapatalk
 

Doesn't the "M" in "MSL" stand for "mean"? An arithmetically computed value of a 'midpoint' in a dynamic system?

Edited November 2, 2017 by Pissed'Ole-Pete

[Hank]

5 hours ago, Pissed'Ole-Pete said:

Doesn't the "M" in "MSL" stand for "mean"? An arithmetically computed value of a 'midpoint' in a dynamic system?

Stand on a beach and determine the water level at high tide. Which wave running up the beach do yiu measure? Uncertainty. Do it again at low tide. More uncertainty. Have two people on two nearby beaches do the same. Variation! Soon the mean will begin to change . . . How many people take measurements on jow many beaches to determine MSL? I have no idea . . . .

[1964-M20E]

The North American Vertical Datum of 1988 (NAVD88) is the vertical control datum of orthometric height established for vertical control surveying in the United States of America based upon the General Adjustment of the North American Datum of 1988.

To the best of my knowledge this is the theoretical MSL at least for the USA.  Yes this is an average construct of a  mean seal level.  Living in south Louisiana roads and front yards can disappear under water in a matter of hours when the wind and tides work together MSL doesn't mean much but seal level does.

Maybe we should start referring to altitude as NAVD instead of MSL.

 

[ShuRugal]

10 minutes ago, 1964-M20E said:

The North American Vertical Datum of 1988 (NAVD88) is the vertical control datum of orthometric height established for vertical control surveying in the United States of America based upon the General Adjustment of the North American Datum of 1988.

To the best of my knowledge this is the theoretical MSL at least for the USA.  Yes this is an average construct of a  mean seal level.  Living in south Louisiana roads and front yards can disappear under water in a matter of hours when the wind and tides work together MSL doesn't mean much but seal level does.

Maybe we should start referring to altitude as NAVD instead of MSL.

 

gotta get some of that NAV D.