The Evolution and Migration of Sea Level Hinge Points

Fig. 1 Gravity hinge between SLR and SLF

I. Introduction

This post is about one particular aspect of The Gravity of Sea Level Change.

That particular aspect is, as the title of today's post alludes to, "the hinge point."

The hinge point is a narrow subject within the larger subject matter which we call "sea level change (SLC)."

The hinge point is a gravity induced, moving, non-imaginary line that is generated by ice sheet mass which in turn generates ice sheet gravity.

That gravity has an impact on sea level, especially near the coast of the land upon which that ice sheet rests, an impact that is "on the move."

The hinge line moves away from the ice sheet as that ice sheet melts and its mass fades into non-existence.

Fig. 2 Hinge Lines circle the globe

In the truest sense, it is the line where one side of that line begins and ends sea level fall (SLF), and the other side of that same line begins and ends sea level rise (SLR).

II. Uses For Hinge Line Knowledge

The hinge line is more than just a scientific curiosity.

It has a very practical application for understanding the dynamics of SLC.

For example, public officials planning construction or remodelling of sea ports, commercial buildings, condominiums, or single family homes where sea level is an issue, need to know whether the sea level in the relevant area is experiencing any hinge point issues (Peak Sea Level - 2).

Another use is categorization of zones as either SLF or SLR, so as to inform residents what is going on.

You might be surprised to know that public officials and others are quite often unaware of what is going on with SLC in their area (Weekend Rebel Science Excursion - 44).

Sometimes, if not all the time, you will not hear about it "on the news" either:

It is uncanny that newspapers in the state of Alaska wonder why the sea level there is falling (Alaska Dispatch News).

(Proof of Concept - 5). Alaska residents are wondering why everyone is talking about SLR when they see SLF at their capital city, and cities near it.

They may be further confused when their state has both SLF and SLR, as that post shows, especially when the hinge point is in their state, and is constantly moving, as some of the graphs in that post indicate:

(Proof of Concept - 5, at Fig. 4, 5, 6 in that post). The hinge line is obviously near Ketchikan, where the sea level has a more even mean average (less SLF / SLR), compared to Juneau.

Juneau, the capital city, is clearly in an SLF mode, whereas, Prince Rupert, B.C., a bit further south near the Alaska / Canada border, is in obvious SLR mode.

III. The Hinge Point Is A Moving Target

The graphic at Fig. 3 shows that the hinge point will move further south, then out of Alaska, as the Glacier Bay area continues to lose glaciers to global warming.

Fig. 3  Glacier Bay, S. America, etc. SLF / SLR

Like the melt-water that disappears into the sea, the "evaporating" ice sheet gravity fades away.

It is then relocated to some other location, as is the glacial ice melt water.

At this time not all of the ice mass has melted or disintegrated into the sea as Fig. 3 shows, because the hinge line is still further north.

Thus, the hinge point is further north at a point somewhere between Ketchikan and Prince Rupert, but will continue moving south.

IV. Software Models Need To Include Hinge Point Dynamics

A. Planning

The current version of the Dredd Blog SLC model has logic that tries to categorize

Fig. 4

PSMSL tide gauge stations as being in an SLR or SLF zone.

The prime reason for that is that SLR logic cannot be applied to SLF locations, and vice versa.

But some locations (see Ketchikan Alaska graph above), are near the hinge point and a determination is not easily made, at least compared to the obvious locations such as Juneau or Skagway, Alaska.

Fig. 5 (S. America SLF / SLR a la Fig. 3)

If software engineers and public officials cannot figure out how to develop logic to detect future SLC dynamics, caused by hinge point movement for example, and thereby figure out what their tide gauges are telling them, how can they face and deal with their civic duties and problems?

This "SLF or SLR?" problem is more difficult than one would think at first blush, as depicted in Fig. 4, Fig. 5, and Fig. 6 examples.

If planners are not aware that as the ice sheet or glaciers melt, the hinge point moves

Fig. 6

away from the coast of the land upon which the ice rests, thereby causing both SLF and SLR over time, they can become confused.

Planners who are aware will know that SLR will stop as the hinge point passes their sea port or coast, then the SLF phase will unsurprisingly set in over time, and finally the tide gauges will begin to show an SLF trend line.

That in itself will not solve any problems, however, but at least the officials will know what they are facing in terms of SLC type.

For example, depending on the SLC type they can then dredge to increase the depth, or raise the docks to match the SLR.

Their comfort at being able to deal with the problem in the short term will fade as the SLC continues beyond the duration of their career and their ability to cope.

B. An Example Software Problem

The software algorithm I wrote to detect whether SLR or SLF is taking place at a particular tide gauge station was, at first, stumped by some of the very close tide gauge station historical records, such as those depicted in Fig. 4, Fig. 5, and Fig. 6.

Thus, it could make a mistake as to whether to calculate future SLF or instead future SLR.

So, it was fine tuned.

Of the 489 PSMSL stations the software selects as suitable for use, out of the 1417 total number of stations,  164 are at first categorized as SLF (the other 325 are SLR).

But then twelve of them (including Fig. 4, Fig. 5, and Fig. 6) are determined to be in hinge line movement scenarios.

The dynamic is that the hinge point is heading their way, but has not passed over them yet.

Thus, even though we can't know exactly when that will happen, because it depends on the ice sheet or glacial rate of melt (which now depends on acceleration by ongoing global warming), we can say that SLF is in that location's future.

The software can therefore calculate future SLF, rather than mistakenly calculating future SLR that will not happen.

V. Conclusion

The more I look into Oil-Qaeda caused global warming induced climate change, (which is creating the SLC armies that are invading sea ports and coasts around the world) the more I am convinced that it is the number one ecological danger to civilization as we know it.

That is because, unlike any human-war invasion, this invader attacks every sea port and shoreline at once (everywhere there is a Pearl Harbor).

Civilization is fighting a battle that it induced, but it is a battle that it cannot win:

• Greenland & Antarctica Invade The United States
• Greenland & Antarctica Invade The United States - 2
• Greenland & Antarctica Invade The United States - 3
• Greenland & Antarctica Invade The United States - 4
• The 1% May Face The Wrath of Sea Level Rise First
• Why The Military Can't Defend Against The Invasion

The next post in this series is here.