Terraforming [Terraforming] Coasts

[Sajjetta]

Hi guys and girls, if Ive missed something glaring please let me know and I'll add it in =)

Intro

The following is everything that I could think of thats relevant to coastal geomorphology and Westeroscraft. The diagrams that are not my own have been chosen as they represent the ones I would have drawn if I had the time. I have square bracketed some locations to check out on the satellite imagery bit of google maps, my screenshots were way to big to upload onto the forum.

I have tried to supply enough relevant process detail to allow builders to form a realistic landscape, but not so much as to get overly bogged down in complex material. In that vain, the first segment starts off quite wordy, and will cover some more general coastal processes which inform the development of coastlines, don't worry there will be lots of nice diagrams later. The second will look at the various choices for builders, in features that are found along coasts and are of a scale relevant to individual builds. The final one will scale up to discuss a couple of landforms that are more or less pre determined by the known geology/landscape. It will then get tied together in a 'how to use all this info' section.

 

[Sajjetta]

1 The Basics

This first segment will be looking at the big picture basics, input factors and the more basic processes which will factor into the later features segment. As a system coasts gave two basic inputs, rock and water. The geology will be looked at in greater detail in the next segment. Water is the powerhouse that does the work. It erodes, transports and deposits material to create coastal features. The source of the waters power is a mixture of wave, tide and alluvial (river) action. Most of the inputs like waves and tide will likely not be seen directly in Westeroscraft but their effects will be, and to understand how best to model these effects some understanding of the cause and process is useful.


A full look at weather and climate is the subject for another post, but wind is key to forming waves which make and break the coast line. So a quick discussion of prevailing wind is required. I see individual projects set a wind for smoke continuity etc, which for the instant snapshot works fine. Coastal features however form over (mostly) long timescales which means features tend to align according to the prevailing wind (There are tradeoffs to be made where powerful storm winds blow from non prevailing directions). So a wider coordination is perhaps needed to keep feature continuity across projects and prevent two neighbouring projects visually contradicting each other on a shared coastline. From the Wall to the south of Dorne is about 1800 miles (rough map work from the wall being 100 leagues long), think Trondheim Norway to Murcia Spain, or Calgary Canada to the Southern tip of Baja California Mexico. On earth this would put it would be partly in the Polar and Farrel atmospheric cells with Westerly winds in the South and Easterlies in the North and a seasonal jet stream orientated anticyclonic mix in the middle. At a stretch it could fit into a single cell to give a single prevailing wind. As we don't know the physics of the planet Westeros is set on (size, rotation, number and thickness of atmospheric cells) its hard to nail down a definite 'it should be this', but there are hints in the book. The description of Stormland storms blowing in from the sea suggests this location receives a predominantly easterly wind, a mirror image of what it would receive on earth. Using earth logic it would become more South easterly as we move south into Dorne. In the North westerlies would prevail becoming north westerlies as you move further northwards. These predominant winds would then get deflected as they flow around the landscape to create some localised variations.

A good little video on atmospheric circulation.

This is what the atmospheric wind patterns would look like on an earth type planet. Below 30N would morror the 30N-60N wind, so blow north to south with some eastward deflection.

Waves are probably the most obvious fundamental aspect to start with. They are created by the wind, and so in many cases there is an inherent relationship between features they create and the prevailing wind direction. They are called waves when being directly created by the wind and this will be used as the catchall term. Incidentally, swell is the term for waves created by an earlier or distant wind. Fetch is the distance a wind blows over water. Waves are bigger and more powerful the stronger the wind is and the longer the fetch is. The breaking of waves as surf and its implications will be shown in more detail later.


Tide height and its associated flow power are also an important source of erosion and deposition, tidal processes and currents dominate with tidal ranges of over 4m, less than that and surf/wave action dominates the shaping of the coastline. Glossing over how tidal bulges are created lets instead focus on how these tides get locally magnified by shoreline shape.

(Watch this if you want to know)

Rising water is the flow tide, its lowering and return to the sea is the ebb tide, assymetry between these can have a complex impact on feature formation. In open mid ocean water on earth, tides tend to be about 1m. At a smaller scale, the magnitude of tides can be strongly influenced by the shape of the shoreline. First, continental shelves play their role,as oceanic tidal bulges hit wide continental margins the flow gets squeezed and tidal height gets magnified. The shape of bays and estuaries also has an impact. Funnel-shaped bays in like [The Bay of Fundy in Nova Scotia] (which has the highest tides in the world 15m) amplify tides. Narrow inlets and prolonged shallow water tend to dissipate them. But narrow inlets also cause a delayed ebb tide as water flow is restricted through the opening causing it to back up. River estuaries at a high flow can also mask tidal action. Wind and weather also have their role. Offshore winds move water away from the coast making the water lower, onshore winds are the opposite piling water up. High pressure weather pushes water surfaces down and away, and low pressure sucks up and in. Something to think about is what state of tide everyone needs to build, it would be close to same across the continent, so would look weird if one person builds a low tide environment, and the person next door goes for high.


As the coast is the interaction between land and sea, sea level change also needs to be briefly talked about. Sea goes up and down with climate, cold means more land ice means lower sea level. Land also goes up and down, this can be because of tectonics, or eustasy (earths crust floats on the mantle, remove material remove weight, land rises up). Something not seen on earth is the lengthy Westerosi seasonality. The long summers and winters may have an effect on sea level, but really we don't know, again its a fantasy world with some unknown rules.

 

[Sajjetta]

Fundemental Processes


There are three processes to be looked at before moving onto coastal landscape features, erosion, the formation of headlands and bays, and longshore drift.


Material erosion takes place through four distinct methods. Hydraulic action, is the physical erosion by the power of water, think flow washing away sand, or a wave forcing air up a crack under immense pressure. Abrasion is the water carried sediment load hitting the erodible surface like shrapnel. Corrosion, water chemically dissolving the erodible material (limestone, salt etc). Attrition, carried load sediment bashing into each other and breaking up. Hence sediment load, make up and water power need to be thought about.


Headlands and bays form where the coastline interacts with alternating bands of soft and hard rock, or occasionally when the sea floods into pre existing low and high ground. When rock banding is discordant the coastline cuts through them as seen in the next figure. The softer rock gets eroded quicker forming bays and leaving headlands, refraction then causes waves to spread out in bays making them less powerful and allowing depositional beaches to form. Refraction also concentrates waves onto headlands causing greater erosion and forming headland features (same principle as why castle gates are best protected on concave walls).


(3dgeography.co.uk)


(Bowen & Pallister, 2001, A2 Geography)

The UK Dorset coast between Poole Harbour and Durdle Door is a pretty classic case study. The north south stretch of coastline shows typical discordant headlands and bays, and the east west section shows concordancy. [Lulworth Cove] shows how bays can form in a hard rock concordant coastline where a weakness in the hard shell exposes a route to the soft rock inland.


(Nagle, 2000, Advanced Geography)



(Southwest Grid for Learning, UK Gov)

Longshore drift is the process by which waves move material along a coastline. The direction of this movement is determined by the relationship between the coastline and the angle at which prevailing waves hit it, wave movement being derived from the prevailing wind. When a wave hits the beach at an angle it pushes material up at that angle, the wave and material then fall down the beach at 90 degrees to the coastline, creating a zigzaggy sideways movement of material along a beach.




(Nagle, 2000, Advanced Geography)

Where theres an obstruction to the flow (harbour breakwaters and groynes, bedrock, headlands, etc) the material piles up against it creating a sawtooth plan view of the beach coastline. [Hove, UK] shows clear west to east longshore drift. There can also be tidal elements to longshore drift features which will be seen later.

 

[Sajjetta]

2 The Coastal Feature Bit

As with anything geomorphological the general outlay of how coast look is determined by the underlying geology and the prevailing environmental conditions which act upon it. Rock type determining landscape, landscape in turn determining slope and available features. For us whilst the general landscape is already determined in shape, slope and rock type, there is a degree of freedom in the finer detail. These 'builder choice' aspects come from the smaller scale geology such as; weaker and stronger bands of rock (caused by localised faulting and banding of different rock subsets within the larger pre determined rock type), sedimentary material available for deposition and local land use. Sediment for deposition (Pebbles, Gravel, Sand and Silt) comes from rivers, coastal erosion, and offshore deposits from submerged past landscapes. Rivers are fairly pre determined, but off shore deposits, and costal eroded material size (to a degree) are builder determined. All this means that there is no fixed dictatorial feature that 'must go here', but a landscape led set of possible features, for a builder to choose from and then 'justify' by detailing the surrounding geology to suit.


There are two basic coastal landscape archetypes; rocky, and not rocky. The formation of these features will broadly speaking be from either landscape erosion, or deposition. Deposition requires, a source of material to deposit, it could occur long term under calm conditions, or rapidly as a storm dumps a load of material. Erodability depends on the strength of the wave/tide acting upon a feature, which includes water velocity and carried material as shrapnel to erode with, plus the strength of the feature its self.

 

[Sajjetta]

Rocky

Cliffs, the big sticky up lumps of rock, are the key feature of a rocky coast and inherently erosional. In short, water hits rock, rock falls down, water removes debris. An active cliff is unstable keeping its steep verticality because it is constantly eroded. Wave action erodes a notch between the high and low water mark, undercutting the cliff. This eventually causes the cliff face to fall, and material get washed away. As the cliff face slowly migrates inland it leaves behind a rocky platform which gets exposed at low tide, think rock pools etc. The speed at which this happens depends upon the power of the waves and the toughness of the cliff. Tide also has an impact, a smaller tidal range means that wave impact is more concentrated and so more effective.


(http://www.geocoops.com/coasts-of-erosion.html)


(Nagle, 2000, Advanced Geography)


(Bowen & Pallister, 2001, A2 Geography)

The bedding of rock strata within a cliff can have a say in its shape too. Vertical bedding would result same as homogenous description above, with different layers just eroding at different speeds. It can also form micro scale headlands if the bedding is discordant. There may be lateral differences as erosion breaks through to the next layer at slightly different times along the cliffs length, like at Lulworth. Horizontal bedding can look different depending on layer toughness and permeability. Soft permeable rock on top of harder rock leads to groundwater flowing along the boundary layer, mod cliff springs and piping. Under heavy rain the lubrication of the boundary can lead to slumping. Soft below hard can lead to to bigger undercuts before cliff fall. Angled bedding sloping away from the sea (like in the diagram) can dissipate wave energy, and towards the sea can amplify it.




(Nagle, 2000, Advanced Geography)


A cliff is 'fossil/relict' when its base can no longer be eroded by the sea, this could be because a beach has formed at the base of the cliff, a large cliff fall has left a lot of material at the base, or perhaps the sea level has changed leaving the cliff high and dry. The top of the cliff will still weather or slump, the bottom will collect all the material thats fallen down, and it stays there because there are no longer any waves to remove it, meaning the cliff becomes less vertical, eventually becoming a stable slope and growing vegetation.


(James Newall) Dawlish, UK


(Wikipedia) Dieppe France, behind the Western Harbour

Cliffs and headlands make for awesome features, caves start in faults and weak spots where erosion is quicker. Caves can erode all the way through to form an arch, Arches roofs collapse to make a sea stack (is it doesn't bring the stack down with it). Stacks erode into stumps.


(OCR)

Caves can erode upwards, or their roofs collapse to form blowholes, where waves crash into the cave and water sprays up and out the hole.


(Wikipedia Diagram)

If this erodes down just right, or the sea level rises, or the cave was underwater, you can end up with features like the blue hole in [Dwejra] Gozo. This is similar to the fresh groundwater cenotes in central America. Caves can also erode through to a dry land basin to create an inland sea, (again google inland sea Gozo). These two plus the former Azure Window arch are all at Dwejra, where the Dothraki wedding was filmed.






Reefs are offshore bars, whilst they can be made of sand and gravel (see bars below) on a rocky coast they are rocky (or coral) subsurface platforms with occasional low tide protrusions. They tend to cause waves to break, and somewhat protect the coastline behind them.

 

[Sajjetta]

Non Rocky


Non rocky coasts are typically depositional in formation. Whether they are actively eroding or depositing at particular time depends on the availability of sediment supply, and the power of the water. Features can be easily sorted and classified by the source or mix of the waters dominant power.



(Daidu et al, 2013, Classifications, sedimentary features and facies associations of tidal flats)


Starting briefly with alluvial dominance we have deltas and estuaries. Deltas have been fairly well covered in the rivers thread, so this is just the brief crib notes. Deltas occur where flow spreads and slows as it enters the sea, causing it to drop its sediment, if the body of water is shallow enough and the river has enough sediment. The deposits build up causing the river to split up into many distributry channels. It can take different forms depending on the alluvial/wave/tide composition. Read the original Galloway delta classification paper for more information, its nice and short. (https://www.researchgate.net/public...phic_evolution_of_deltaic_depositional_system )



(Smithson, Addison & Atkinson, 2008, Fundamentals of the Physical Environment)


Estuaries are where the mouth is a tidal inlet, the brackish water can lead to salt marsh banks, and the sharp bend they create in the coastline can lead to the formation of spits and other features.

 

[Sajjetta]

Beaches (strand plain) are deposited material found on wave dominated coastlines, usually sand or pebbles and often sourced by off shore underwater bar deposits, topped up by eroded coastal and river material. Beaches are built and destroyed by breaking waves, how a wave breaks is dictated by beach slope and water depth and can vary along a beach and with tide so a single beach can display depositional and erosive features. There can also be seasonal variation with winter storms eroding beaches and moving sediment out to offshore bars, and summer waves transporting the bar material back to the beach.


Constructive waves build beaches with a stronger beachward movement (swash), destructive waves destroy them with a stronger backwash.


(Nagle, 2000, Advanced Geography)

Wave type depends on beach slope water depth and the energy it gains as it travels across the ocean, longer wave travel and stronger wind, more energy. Collapsing, and spilling waves keep forward momentum and are constructive, pushing material up the beach. Plunging waves scour the bed in an erosive manner. Spilling waves are often considered as failed plungers and are fairly neutral.


(Smithson, Addison & Atkinson, 2008, Fundamentals of the Physical Environment)

Beaches form ridges called berms at the upper reach of wave swash. A series of ridges can form down a beach profile, ie low tide, high tide, storm surge. Cusps are regular crescent shapes found in the swash/backwash of a beach. They develop best on mixed grain size beaches, with a high tidal range and waves approaching at right angles, with coarser material being found on the cusps horns.


(Smithson, Addison & Atkinson, 2008, Fundamentals of the Physical Environment)


(Nagle, 2000, Advanced Geography)

 

[Sajjetta]

Moving onto the plan view there are several features created by beach deposits.


(Bowen & Pallister, 2001, A2 Geography)

Spits can form at significant bends in the coastline such as sharp cornered bays and river mouths that aren't alluvialy dominant. Here long shore drift allows a beach to continue building the beach line even though the land behind bends away. The hook at the end of the spit is formed by a significant secondary wind direction, its possible for a spit to develop a series of hooks. Behind the beach front there are often dunes, and then salt marsh on the sheltered leward side, progressing into tidal flats as the back of the spit is protected from waves and thus is tidally dominant (if it were alluvialy dominant the spit would get washed away by the river.


(TheBritishGeographer, based on Southwest Coastal Group)





Double spits can be created by two opposing dominant winds, or an asymmetric dominance of flow tide into an embayment, such as below where the sea is to the south and the bay to the north. Another method of double spit formation is by splitting a bar.


[West Wittering Beach, UK]

When a spit completely blocks off an embayment it becomes a bar, the water trapped behind it becoming a lagoon. Beach bars can also be created by the mass onshore migration of an offshore bar.




Tombolos are beach bridges from an island to the main coast. This is caused by deposition on the leeward side of the island eventually building a beach out towards the mainland, with calm and shallow enough water a tombolo is eventually formed. It is also possible for spits to grow out to islands like [Chesil Beach, UK] or [Mt Maunganui NZ]


(Worldatlas.com) Angel Road, Japan

Where two opposing longshore drift directions meet cuspate forelands can be formed. An example of this is [Dungeness UK] where waves from the Atlantic and the North Sea converge, it is also the convergence point for the tides from two seas. Wave convergence can also occur on the leeward side of islands where waves refract round to meet each other. Cuspate forelands tend to take up an onion layered appearence as more layers of material get added.


A barrier beach is an offshore bar that remains unsubmerged at high tide. It some what protects the coastline behind it, and can end up vegetated and fixed. Otherwise they act like submerged offshore bars and can migrate.


Sand dunes can form behind beaches with enough sandy material, I'll cover dunes in full another time as theres a lot to them. Just remember they are wind formed, so material must be small enough to be carried by the wind but not so small (silt) that it blows away entirely. Beach turns into embryo dunes, then behind are larger mobile dunes. These get fixed into by marram grasses, then eventually shrubs and pines. The Dutch and Danish coastlines are good to look at. The diagram below shows dune type and plant species. The fore dunes/ yellow dunes are usually the tallest as they have best acces to new sand being blown in. The windward side of a dune tends to be less steep than the leeward side, lose sand doesnt get steeper than 30 degrees, and fixed vegetated sand 45. The dune ridge will be perpendicular to the prevailing wind which created it.


(Kate Bewley, Bull Island Biosphere Reserve)


(Nagle, 2000, Advanced Geography)

A raised beach is a beach that has been left high and dry by lowering sea levels. This can be seen as still loose material, or a rocky sandstone platform where the loose top material has been removed to reveal the more consolidated material below.

 

[Sajjetta]

Tidal flats are unsurprisingly tidal and flat. Flooded at high tide and exposed at low tide. As the water flows in and out it crates meandering river like channels. And on the fringes of the flat salt marsh will grow. Working up from the low tide mark we start with unvegitated sediment flats, then come sparse pioneer species (Worms, Clams, cord grass), towards the high tide mark and regularly inundated by the sea we get the dense low marsh (Sea worts, Sea aster, Festuca grass, Sea purslane), above the normal high tide and up to the spring high tide there is saltmeadow and its associated grasses, beyond that are saline adapted climax species (shrubs and trees). On the coast desolate flat gives way to The fringe of the lagoon in [Venice, Italy] is good to look at, some of the channels have been artificially straightened, but the patch by the northern end of the airport is pretty good. Mangroves are a tropical form of saltmarsh.


Venetian Marsh

 

[Sajjetta]

3 Scaling Back Up


Here is a brief look at a couple of coastal features which would cross multiple builds and are pre given from the shape of Westeros. This section is designed more as a jumping off point for further research.


The larger scale features that bear some relevance but are yet to be discussed are fjords and rias. Both form in the same way as sea level ruse floods a pre existing coastal valley, the difference being how that valley formed in the first place. Fjords are created when glacial valleys flood, creating deep steep sided inlets. The majority of the coast of [Norway] is the classic example here, the west coast of Scotland, British Columbia, and NZ South Island, are also worth a look. Fjords are worth mentioning as the coastline of the vale looks typically Fjord like.


A ria is the flooding of a river valley, they tend to be shallower less steep and shorter than their ice carved cousins. Noteable rias to have a look at; Chesapeake Bay, the Dalmation Coast, all along the coast of Galecia Spain, same for Brittany France, Sydney Harbour Australia. They are often tidally dominant. There are a few spots along the Westerosi coast which could well be Rias.

 

[Sajjetta]

How to use this information


So how can westeroscraft builders translate this all into the build?


Look at the pre determined landscape, coast shape and rock type. Work out your predominant wind direction (and probably try to agree it with your coastal neighbours for continuity). These should give you a clue as to sediment supply, rocky vs non coast, and alluvial/wave/tide dominance (not so hard and fast so there are mix options here that can be backed up by builder added detail), and thus the type of features available to you.


Tweak your geology subsets to suit the exact feature you want to put in an exact location, soft rock, hard rock bedding, faulting, erosion, beach material type, offshore bars. Where possible (in a minecraft world) add the environmental details that support your choice of feature.


Hope this is helpful.


Sajj