Showing posts with label Coastal Geology. Show all posts
Showing posts with label Coastal Geology. Show all posts

Saturday, April 03, 2021

Geology Through Literature - Han Christian Andersen's: Vano and Glano

Geology Through Literature: 

Hans Christian Andersen's: Vänö and Glänö (1867)



For the seventh entry we continue on through Hans Christian Andersen's oeuvre to our next geological reference.

For other Geology Through Literature entries, please check them out compiled on my website.

Vänö and Glänö (1867)

Shoreline Geology

Near the coast of Zealand, off Holsteinborg castle, there once lay two wooded islands, Vänö and Glänö, on which were villages, churches, and farms. The islands were quite close to the coast and quite close to each other; now there is but one of these tracts remaining.

One night a fierce tempest broke loose. The ocean rose higher than ever before within man's memory. The storm increase; it was like doomsday weather, and it sounded as id the earth were splitting...

That night Vänö vanished into the ocean depth; it was if that island had never existed. But afterward on many a summer night, when the still, clear water was at a low tide, and the fisherman was out on his boat to catch eel by the light of a torch, he could, on looking sharply, see Vänö, with its white church tower and high church wall, deep down below.

...

You went away from there ... and after a few years you have returned.... Where is Glänö? You don't see little wooded island before you; you see only open water. Has Vänö finally taken Glänö, as it so long was expected to? On what stormy night did this happen, and when did an earthquake move old Holsteinborg so far inland?

There was no stormy night; it all happened on cleat sunny days. Human skill built a dam to hold back the ocean; human skill dried up the water and bound Glänö to the mainland. The bay has become a meadow with luxuriant grass; Glänö has become part of Zealand. 

If you try and search for the word "Glänö", most of the results are just for references to this specific story. However, I was able to find a bit for information after doing a search for the Holsteinborg castle, which does exist. 

Google Maps of Holsteinborg Castle showing Glænø Island.

Based on the map of the castle, there sure enough appears to be an island, directly next to Holsteinborg Castle called Glænø. I feel this is far too close a coincidence to be happenstance. However, in the story, it specifically states that the island of Glänö was dammed up and incorporated into the mainland. Even though the map above doesn't appear that the island is not an island, let's look at the aerial photo to see if things get any clearer. 

Aerial Photo of the area around Holsteinborg Castle. Image courtesy of Google Earth. 

Here we can see a lot more sediment build up in the estuary behind the island, and that is because of the dam that is built to the island. In the picture here and above, the road that leads to the island on the northwest corner is on top of a 100 meter long dam. So, as the story stated, the residents built a dam, essentially merging the island with the mainland.

But where could Vänö (also spelled Vænø) be then?

There are a couple of theories that I have. My first theory is that the island directly next to Glænø, Østerfed could be a new name for the island. However, since this is clearly still an island, my guess is that this is not what we are looking for.

If this is not Vänö, then the island must once have resided within the bay to the south of Glænø called  Smålandsfarvandet. If we look a bit further out from Glænø into the bay, there is an island with a similar sounding name.

Smålandsfarvandet aerial image courtesy of Google Earth.

The island, Vejrø, does have a similar name, however based on the description, the island is not really "quite close", nor "near the coast". It is also not a sunken island. So, my last theory is that the island truly was sunk off the coast somewhere. But if it was, there is likely evidence in the bathymetry of the bay. There should be some sort of raised island under the water, as other parts of the text describe that the island is still visible on calm water days.

Although there are not a lot of publicly available bathymetry charts of Smålandsfarvandet, I did find a few that offered glimpses that there is a submerged land area about halfway between Glænø and Vejrø. As can be seen in the following bathymetry chart. 

Bathymetry map off the southern shore of Glænø. Image courtesy of Kroon et al., 2015.

A little further investigation and it turns out this shallower area of the bay on the southern edge of the map above is actually a reef. It is known as the Kirkegrund Reef and parts of the reef reach as low as 1-2 meters below sea level (~5 feet). 

Cross section of the Kirkegrund Reef. Image courtesy of Stæhr et al., 2016.

The cross section above shows shallow areas around 6 meters below sea level, however other maps show a significantly shallower region in other parts of the reef. The further back in time that we go, the lower sea level was, so perhaps this was the island that Andersen was referring to. If we think that this island was once Vänö, then it is possible that legends grew up about this island off the coast that eventually was swallowed up by a big storm. And the things that the fishermen were seeing off shore was actually the reef far below the surface and not the remnants of various buildings once build on the island.

at No comments:
Labels: , ,

Thursday, April 01, 2021

Geology Through Literature - Han Christian Andersen's: A Story from the Sand Dunes

Geology Through Literature: 

Hans Christian Andersen's: A Story from the Sand Dunes (1859)



For the fifth entry we continue on through Hans Christian Andersen's oeuvre to our next geological reference.

For other Geology Through Literature entries, please check them out compiled on my website.

A Story from the Sand Dunes (1859)

Shoreline Erosion
Still, it is easy to imagine yourself back in times more remote than even the reign of Christian VII, for now, as then, the brown heath of Jutland stretches for miles with its barrow, its mirages, its winding, rough, sandy roads. To the west, where broad streams flow into the fjords, there are marshes and meadows, encircled by the high sand hills which rise up toward the sea like an Alpine chain with jagged summits, broken only by high banks of clay. From these the waves eat off giant mouthfuls year after year, so that the edges and summits topple down as though shaken by an earthquake. That's how it looks today, and that's how it looked many years ago...

 The passage describes the persistent erosion along the western shore of Jutland, a region of Denmark, with Western Jutland bordering the North Sea. 

Map of Jutland, Denmark. Image courtesy of Wikitravel.

The beaches and the sand dunes of the Jutland coast were deposited during the last Ice Age consisting of clay and fine sand that total 100 meters of sediment deposited over 100,000 years. These deposits are known as the Skærumhede series.

The Jutland western shore. Image by Lucia Margheritini and courtesy of Science Nordic.

These sediments make up much of the western coast, but they are slowly being transported out to sea due to coastal erosion. As the cliff faces are worn away at the bottom, the upper layers eventually collapse and then are carried away by the waves. Much of the erosion occurs during the winter months when the water levels are higher and storm levels are stronger, producing winds and waves capable of wearing away at the cliff face that is otherwise out of reach during calm, summer days. 

The sediment along the coast is then transported through the longshore current from south to north. However, the amount of sediment removed is more than the sediment supplied by the current, so the coastline is in a losing scenario. It is estimate that it has been in a losing scenario since the last ice age, ~10,000 years ago. 

And although this erosion has been continuing since long before and after Andersen's time, the current rate of erosion has been increasing. There are several reasons for this but mainly they can boil down to manmade impacts and climate change. Structures on the beach, scientists know, have a tendency to alter the erosion patterns, often producing more erosion in areas beyond where the structure are built. Think dams and sea walls. These structures stop erosion where they are built, but the lack of sediment within the water beyond these points allows for more erosion than would otherwise occur. With climate change there are many reasons for potentially accelerated erosion including: more and/or stronger storms, rising sea levels, and changes in weather patterns. It is estimated in this region that the changes in weather patterns, specifically more rain, has been the cause of the accelerated erosion, with the increased rain breaking down the cliff edges more readily than they were before. 

References
at No comments:
Labels: , , ,
Subscribe to: Posts (Atom)