Talk:Hypsometry

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Untitled

Can someone please elaborate on "On Earth, the hypsometry is bimodal, while on Venus it is unimodal."?

Added a brief explanation. Is that better? Astronaut (talk) 23:20, 1 April 2009 (UTC)[reply]

Great, worlds better! Thanks. —Preceding unsigned comment added by 38.117.109.20 (talk) 00:26, 3 April 2009 (UTC)[reply]

Unimodal hypsometry?

The article says other planets' elevations are unimodal generally due to lack of oceans. That seems to imply that we don't use hypsometry on other planets, since it conflicts with our definition of being "relative to mean sea level". It would be helpful if the article stated this explicitly or otherwise clarified. --Pythagimedes (talk) 20:10, 10 December 2020 (UTC)[reply]

True. I did actually edit the definition to clear up a separate issue. (It implied that Hypsometry was a measure of land elevation but not sea, when really it is both.) Other planets would use their equivalent vertical datum (zero-elevation surface). For instance, NASA's Mars Geodesy/Cartography Working Group recommends using the equipotential surface determined from Mars Orbiter Laser Altimeter (MOLA) data as the reference for elevations. Whether that's very useful information to include is quite another matter, however. PeregrineFlight (talk) 02:12, 22 May 2021 (UTC)[reply]

The Reason for Eath's Bimodal Hypsometry Curve

"On other planets within this solar system, elevations are typically unimodal, owing to the lack of oceans on those bodies." I am not a planetary geologist, but from my understanding, this is pointing to a spurious variable. My understanding is that it is the difference in density between continental and oceanic crust that results in this bimodal distribution.

For oceanic crust, its thickness is determined by the density of the basaltic rock which composes it, due to isostatic equilibrium. This gives oceanic crust an average thickness of 6-7km, which determines the average depth of the ocean floor. Since oceanic crust is subducted and recycled quite quickly on geologic time scales (on the order of 100-200 Ma), it generally remains fairly close to that average.

For continental crust, David Rowley suggests in a 2013 article that its dominant modal elevation is set at sea level due to both erosion (on land) and deposition (underwater) acting concurrently to increase the area at that elevation.

PeregrineFlight (talk) 01:26, 22 May 2021 (UTC)[reply]

I now found a source confirming this and corrected the page. PeregrineFlight (talk) 17:07, 23 May 2021 (UTC)[reply]