The Emperor Seamount Chain and the Hawaiian Ridge.

Plate tectonics is a very well established theory, and can explain the vast majority of geological features present on our planet. In the Pacific Ocean, however, a number of islands are present which are not all a direct result of plate tectonics but instead are related to convection occurring within the mantle.

Perhaps the most well known of these volcanic islands are within the US state of Hawaii (In this text I use Hawaii to refer to the state as opposed to the Big Island, Hawai’i). From looking at the ocean bathymetry around Hawaii it is very noticeable that there exists a long chain of seamounts towards the north west of the islands in varying states of erosion – these are the seamounts of the Hawaiian ridge. Further in the north west this chain diverges northwards, forming the Emperor Seamount Chain.

Google Data SIO, NOAA, US Navy, NGA, GEBCO, Data LDEO-Columbia, NSF, NOAA. 20°12'50''N 157°00'10''W 1,434.2km
Image of Hawaiian Archipelago (Google Earth)

These volcanic islands, and the seamounts behind them, are the result of a large hotspot below the Pacific plate. This hotspot means that the geothermal gradient below the oceanic crust is shallower than it would usually be, and so there is thinning of the lithosphere. This increased temperature leads to melting of the mantle, which becomes less dense in the melt regions and rises up. The melt rises until it reaches a level of buoyancy, at which point it can pool and solidify. In some regions, however, this magma continues to rise until it reaches the surface. At this point it is able to pour out, and form layers of very shallowly dipping basalt – producing a shield volcano.

Hypothetical Side Profile of a Shield Volcano
Hypothetical Side Profile of a Shield Volcano

In the Hawaiian archipelago these shield volcanoes have grown to be massive. The largest of these at the moment is Mauna Kea, towering a collossal 10,200m above the seafloor (4,207m above sea level). Only two of these volcanoes are currently active – Mauna Loa, and Kilauea.

The formation of new volcanoes is generally a result of the motion of the Pacific plate as opposed to that of the hotspot. For the past 40 million years the hotspot has likely been relatively stationary, while the Pacific plate has moved north west – so the chain of volcanoes has moved south east. Once the volcano moves away from the hotspot it becomes extinct, and the rate of growth is outweighed by the rate of erosion – and so it erodes away leaving a small seamount. Over 40 million years ago, it is believed that the motion of the hotspot southwards combined with the continued motion of the Pacific plate led to the different direction of motion of the Emperor Seamount Chain – the hotspot becoming stationary 40 million years ago led to the change in direction.

Google Data SIO, NOAA, US Navy, NGA, GEBCO, Data LDEO-Columbia, NSF, NOAA
The Emperor Seamount Chain and Hawaiian Ridge from Space. The prominent change in direction is visible (Google Earth)

As a result of the low viscosity of basaltic lava (resulting from the low silica and low crystal content) the lava flows are able to travel far and wide. It is this wide spread of lava which leads to the shield like profile of these volcanoes. On the islands which currently have active volcanism, a range of different lava flow style can exist. The most common of these are the a’a and pahoehoe lava. a’a lavas are characterised by a high volume flow rate with large channels containing thick flow units of high viscosity. On the extremities of the flow this lava begins to crystallise, and as this skin is broken up it leads to ‘clinkers’ which can fall off and produce an underflow to the lava flow.

A’a Lava Flow on Kilauea (USGS)

Pahoehoe lavas, conversely, have low volume flow rates and a low front flow velocity. These have much lower viscosity, and as a result of the lower velocity can build up a skin which is non disrupted, and is able to form lava channels through which the lava can flow relatively unhindered. When expressed on the surface these lavas show a ropey texture, on the order of 0.2-2m thick.

Cooled Pahoehoe flow showing ropey texture (USGS)
Cooled Pahoehoe flow showing ropey texture (USGS)

Many of the islands formed in Hawaii archipelago have large volumes. Mauna Kea, for instance, is approximately 3,200km3, and this massive volume leads to a large weight pressing down on the oceanic lithosphere. This loading is ‘compensated’ by the deformation of the elastic lithosphere, leading to flexure. It is this flexure which produces a moat around the islands, with raised ridges on the extremities. This can be observed in the following satellite image.

Effect of Loading on Bathymetry. Directly around the load there is a moat, surrounded by an elevated area. On a long wavelength this is elevated above the typical oceanic crust due to the hotspot.
Bathymetry around part of Hawaii. (School of Ocean and Earth Science and Technology, Hawaii -
Bathymetry around part of Hawaii. (School of Ocean and Earth Science and Technology, Hawaii – Shows depression immediately around island.

The manner in which these islands have formed has had a large impact on the range of wildlife which can exist there. Hawaii (and the other Polynesian islands) are typically many hundreds if not thousands of miles away from neighbouring landmasses, which combined with the short period of time they’ve existed there for has limited the range of organisms which have been able to reach and establish themselves there. This leads to a unique ecology present on the island, which is primarily dominated by flying and marine animals.

Monk Seal Mum and Baby, showing folds of skin (NOAA, found on Marine Conservation Institute Website)

A number of marine animals live in the seas around the Hawaiian islands – including, for example, Humpback Whales, Spinner Dolphins, and the northern relative of the Elephant Seals found around Patagonia – the Northern Elephant Seals. Perhaps one of the most interesting of these marine animals are the Hawaiian Monk Seals, as it is one of only two mammals found natively in Hawaii. These are dark gray seals, named Monk Seals after the folded skin covering their heads. These seals feed on lobsters, eels, and fish which live on coral reefs around the atolls and islands, and can grow to 170-230kg – they are sexually dimorphic, such that females are typically larger than males.

The life habits of these seals mean that they are very susceptible to disturbance by human activity. Typically they can only be found on remote islands which have very little human impact, as fisheries and other predators compete with them for food. The impacts of climate change on the coral reefs from which they obtain most of their food are likely to also impact these seals.

Hawaiian Hoary Bat. (C. Pinzari, found on USGS website)

The other native mammal found on Hawaii is the Hawaiian Hoary Bat. This is a small bat with a wingspan of around 30cm which weighs about 14-18g. They have brown-gray coats, and white tinged ears. Hawaiian Hoary Bats typically live from sea level to ~2200m, however they have been observed higher than this. It is likely that they roost amount trees near forests on various Hawaiian Islands.

These bats are one of many flying animals in Hawaii, others of which include the Laysan Albatross (a large white and black seabird which feeds far from its breeding colonies) and the Hawaiian Noddy (a medium sized abundant tern).

Since humans arrived on these islands they have brought with them a range of species from outside, such as the Axis Deer (native to the Indian subcontinent, which has been introduced to the island of Lanai) and the Feral Wallaby (originally having escaped from a zoo). Humans have impacted the islands in other ways too – large amounts of the coral present have undergone bleaching, as a result of increased ocean acidification and waste runoff.


"Cerro Torre and Fitz Roy from Ruta Provincial 23 to El Chaltén" by Miguel Vieira is licensed under CC BY 2.0

Patagonia. A beautiful region of South America, often ignored against the prominence of the Amazon Rainforest. Yet, while perhaps less biologically diverse, a number of abiotic factors have led to the development of a diverse set of features across the region.

The header image, “Cerro Torre and Fitz Roy from Ruta Provincial 23 to El Chaltén” by Miguel Vieira, is licensed under CC BY 2.0

“Andes backyard” by Kevin Rheese is licensed under CC BY 2.0

As with the majority of South America, perhaps the most apparent geological feature is the Andes, a vast mountain range stretching from the top to the very bottom of the continent. This range influences the climate, and hence the environments, which develop in its neighbouring areas. To the east of Patagonia, for example, lies the Patagonian Steppe, an ecoregion covering a vast 487,000km2 featuring predominantely shrub lands, grasslands, rivers and lakes. As a desert, this area sparsely experiences rain due to the inhibition of the westerly flow of moisture from the Pacific leading to the formation of a rain shadow.

In spite of the aridness of the Steppes, it is not in any way void of life. As in the majority of other deserts around the world, a number of well adapted reptiles such as the Patagonian Gecko (geko patagónico), and lizards such as Liolaemus fitzingeri. More than 100 bird species reside on the Steppe, including the Lesser Rhea – a large flightless bird similar to the Ostrich and Emu (possibly having originated from an ancestor common to these groups when the three continents were connected in the supercontinent Gondwana).

“Lesser Rhea” by Federhirn is licensed under CC BY-NC 2.0
“GUANACO” by cuatrok77 is licensed under CC BY-SA 2.0

While deserts are typically viewed as hot places such as the Sahara and Gobi, this is a much colder desert. With winter temperatures of around -2°C, the animals living here have had to evolve various strategies to deal with the extreme conditions. This is shown very well in the Guanaco, a mammal related to the camel. These are the largest herbivores (browsing grasses, shrubs and lichen) in the region, and have thick wool coats which are dark on the top and white on the bottom – the darker colours likely helping to absorb incident heat, while the white inhibits the cooling effect of the ground. Thick eye lashes are present, which help the Guanaco against the dust present (kicked up by west winds blowing during the summer).

From these Guanacos the Llama and the Alpaca have been selectively bred and domesticated for wool, meat and skin. Between 1,000,000 and 2,200,000 are believed to live within the Patagonian Steppe.

West from the Steppe lies the Andes, framed by the thin green strip of the Andean-Patagonian forests. These are the southernmost forests in the world, and have likely been present for the past ~45 million years. The forest covers ~98,000km2, and is one of the largest isolated forests – blocked from the east by the Steppe and to the west by the Pacific, the Andes, the Atacama, and the Chilean Coastal range. Due to this, little mixing has occurred with other forests, and thus it has differed from other forests around the world. For instance, it has large numbers of flowering plants in contrast to the usual dominance of conifers.

The Andes themselves are the longest continental mountain range in the world, at about 9000km long. A simplified story of their formation begins with the end of Triassic, and the end of Pangaea. As Pangaea rifted, the area to the west of the Andes rifted apart from the east. This rifting led to the formation of a back arc basin which later collided with South America. This back arc collision led to the beginning of the formation of the Andes, approximately 30Mya (The actual story is a lot more complicated than this – this is overly simplified).

As a continuation of this formation, there is a subduction zone under the coast of South America, where the Nazca plate is subducting under South American plate. To the south there is a triple junction between the Nazca, South American, and Antarctic plate. The story is further complicated by the fact that the East Pacific Rise (a spreading centre) is subducting beneath South America. As you would expect, this complicated story has led to a lot of active faults along the extent of this west side of South America, which caused the 2010 Chilean Earthquake and the 2007 Peruvian Earthquake. Similarly, it is the hydration of the mantle above this which leads to the formation of magma chambers in the crust below, leading to the formation of volcanoes along this arc, and the formation of geysers such as the El Tatio – one of the highest geyser fields in the world.

Two of the mountains in the Andes are Cerro Chaltén and Mount Hudson. The former is located in the Southern Patagonian Ice Field in Argentina and is named for the HMS Beagle Captain Robert FitzRoy (notably, the ship which took Darwin to South America where he famously developed the theory of evolution!). The latter, technically a volcano, was the site of one of the largest eruptions in the 20th century (It was overshadowed by Mount Pinatubo, however) in 1991. Luckily the area was evacuated and so nobody was killed, unlike an earlier 1971 eruption which while it was weaker (VEI3 instead of 5), caused lahars killing 5 people. This mountainous region also contains one of the worlds only advancing glaciers – Glaciar Perito Moreno. The reason for this is as yet unknown.

“Los Glaciares National Park” by Jorge Láscar is licensed under CC BY 2.0

The Andes themselves, while rather barren (in the higher reaches) are not at all void of life. Guanacos are still present, however the Andes are notable for their birds – with over 400 species present! A notable bird species in South America is the Andean Condor (Vultur gryphus) which is a species of condor with the largest wingspan of any flying bird in South America – a whopping 3.2m! They have the largest wing area of any bird. The Andean Condor is the national animal of Colombia, and is one of the largest birds of prey at 20-25 pounds – though males are larger than females, as these birds show sexual dimorphism. Unfortunately, in 1973 they were added to the endangered animal list as a result of over hunting, being shot by farmers, and their food being poisoned. As the condors are scavengers, they primarily eat carrion – so when this was poisoned (say by farmers) it affected the birds. They inhabit high mountains, low deserts, and alpine in Venezuela, Colombia, Peru, Argentina and Chile, and unlike many other bird species they don’t build nests, preferring instead to lay eggs among borders in order to conceal them from sight.

“Magnificent Andean Condor” by Pedro Szekely is licensed under CC BY-SA 2.0

Further west from the Andes lies both the Atacama desert and the Chilean Coastal Range. While not technically in Patagonia, the Atacama desert is rather interesting as it is the world’s driest non polar desert, due to being entirely closed off by both the Andes and the Pacific Ocean’s Humboldt Current. This dryness leads to salt pans and dry barren rock formations, with cloudless nights (Large numbers of telescopes are present to take advantage of this!) and no light pollution. The temperatures can range from 5C to 40C, likely in part due to the dryness of the atmosphere reducing its ability to buffer the temperature.

The incredible dryness of this area gives itself readily to comparisons with Mars – so much so, that the Atacama Desert is used to explore the suitability of life to survive on Mars, and to test cave detection programs for Mars – such as the Earth-Mars Cave Detection Program. It also makes it a useful place for solar power. The lack of moisture means there are almost always clear skies and so large amounts of sunlight – which is exploited by projects such as the $1.1bn Atacama 1 Concentrated Solar Power Plant (Planta Solar Cerro Dominador).

The Chilean Coastal Range faces onto the Pacific ocean in areas and is as a result of aligned uplifted blocks along the coast, which were separated from the Andes. At the moment this area shows no sign of volcanic activity.

Patagonia is flanked by oceans – the Pacific ocean to the west, the Atlantic to the right, and the Drake Passage in the Southern Ocean to the south. These are inhabited by a range of creatures, such as the Magellanic Penguins (Spheniscus magellanicus) and the Southern Elephant Seals (Mirounga leonina).

“Magellanic Penguin” by Don Faulkner is licensed under CC BY-SA 2.0

Magellanic Penguins are a species of penguin which is only found in South America. Approximately 1,600,000 breeding pairs exist, in loose colonies around areas such as Golfo San Matías, Tierra del Fuego and Puerto Montt. These penguins, like many others (notably excluding Emperor penguins) breed over the summer – which in the southern hemisphere involves breeding in September and laying eggs in October. Typically two eggs will be laid, followed by a 40 day incubation. Incubation is split equally between the mother and father while the other parent goes off to forage for food such as anchovies and sardines.

Changes to the environment around them due to climate change, fishing and oil pollution have greatly affected these penguins. This is shown in how a typical breeding pair would usually produce ~1.5 chicks, yet in the Falklands due to the limited availability of fish only ~0.5 chicks are able to survive through childhood. Other ways that climate change might affect these beautiful creatures is in their site fidelity. As the sea level rises, this may lead to traditional colony areas being flooded, harming the survival of the penguins.

“Southern Elephant Seal on the beach” by Liam Quinn is licensed under CC BY-SA 2.0

Magellanic Penguins are predated upon by Southern Elephant Seals, which live in the cold yet fish rich seas of the sub Antarctic and Antarctic waters. These are the largest type of seals, with males growing up to 4.5m long – though they are sexually dimorphic and females only grow to around 2.8m. While the Penguins are monogamous for life, the elephant seals are somewhat more… promiscuous. Males battle for harems of 40-50 females in often violent fights. These females give birth in late winter (Approximately September), and after an 11 month pregnancy give birth to young who then suckle off of their blubber.

Similar to the penguins, however, the seals have been negatively impacted upon by human activities. During the 19th century these majestic creatures were hunted for their oil and blubber, a process which only ceased when this was outlawed in 1964. Following the banning of this hunting they have rebounded to almost 600,000 individuals with an almost circumpolar distribution.

The complex geology of Patagonia has had massive impacts upon environments and ecosystems which have developed, however human actions look set to seriously harm many of the amazing creatures who live in these areas. Some progress has been made – the regulation (1910, licenses required) and later prohibition (1964) of hunting Southern Elephant Seals, for example. However, more needs to be made if this amazing area is to be preserved.

The Yorkshire Dales

In 1954 a large chunk of Yorkshire (now Cumbria) was sectioned off to produce the Yorkshire Dales National Park. The National Park today is visited by millions of visitors and farmed on by hundreds of farmers, however over the preceeding millenia this area has been affected and changed by a large number of factors, some of which have been introduced below.

The vast majority of the Yorkshire Dales landscape is dominated by limestone from the Carboniferous, which on the higher fells is typically capped by Millstone Grit. A look at a geological map of the area shows, however, a slight discrepency in the North East of the region – instead of the typical limestones, a large number of mudstones and sandstones can be found. These are Silurian in age, and have been brought up level with the Carboniferous limestones by the large Dent Fault.

Geological Map of Yorkshire Dales (From BGS Geology of Britain Viewer)

The different rock composition here reflects the changing depositional environments this land mass has experienced. For instance, the Silurian mudstones and sandstones suggest a relatively deep sea environment, which was unable to carry much sediment. This meant that only fine grained particles were able to be entrained and deposited, producing the mudstones. The fauna in this mudstone can vary from being purely composed of graptolites and planktonic organisms which suggests that the lower reaches were predominantely anoxic, to regions where burrows can be found which imply oxygenated soils. This reflects the variation in sea level during the Silurian and Ordovician time, likely related to the Ordovician glaciation.

Location of continents during Silurian. (USGS)

On the other hand, the Limestone of the Carboniferous, almost a hundred million years later, suggests far warmer, shallower seas in a tropical climate. Corals, trilobites, crinoids, and brachiopods can all be found in these rocks which suggest that it was a very well occupied environment. Younger rocks atop these often can be found to contain sandstones and coals from coastal swamps of giant ferns.

Continents during Carboniferous (USGS)

The variation in the rocks across the Dent Fault also has an impact on the geomorphology of the landscape. In the Silurian mudstone bedded environments, the hills tend to be taller and steeper – this is related to how the mudstone is less able to be eroded by acid rains and other flows. The basic limestone reacts with acid rain (as is used by geologists to test for them!) and so over thousands of years they have been chemically eroded. As bogs tend to occur where there is water at the ground surface, nutrients are scarce and the ground surface is acidic these tend to be found predominantely in mudstone areas, which helps to obscure these outcrops from view.

In the Carboniferous areas there is often a large amount of exposed outcrop. Shake holes can often be seen, generally as a result of collapsed caves; The karstic limestone often forms subterranean caves and underground rivers (aiding its drainage ability) which are susceptible to collapse.

This variation in underlying bedrock in this area is very well demonstrated around Taythes Gill. Here, as you traverse east to west along the Gill you start off in fine grained muddy sediments, which all appear to be dipping in a general westerly direction. The quality of this mudrock decreases as you reach the fault zone, after which the carboniferous limestone can be found. Close to the edge this is often found modified to dolomite (the damage done to both sides around the Dent fault is likely related to the extent of movement across this boundary). Beyond this, the limestone appears to still be dipping west but it gets less steep as you progress along. This can be related to the motion of the fault, as demonstrated in a sketch below.

Taythes Gill geological map (from BGS Geology of Britain viewer)
Simple schematic showing an interpretation of the faulting in Taythes Gill

In addition to the large Dent fault, a number of smaller folding and faulting incidents have taken place and been kept in the geological record. For example, along the stream from Taythes Gill there is a large well exposed anticline, and in the Fell End Clouds there is another large anticline. The effect these folds and faults can have on the economic viability can be seen both in the Fell End Clouds, and in the Caldew Valley (Which is actually in the Lake District, but is very similar – in simple terms there has been a granite intrusion and post dated faulting, leading to veins).

Taythes Gill Limestone Anticline
Fell End clouds fold

When rocks fold or fault, they can crack. These weaknesses can then be filled under pressure by minerals, leading to features such as quartz veins, or calcite veins.

Cracked limestone with calcite veins.

These veins can contain a range of different mineral ores depending on their location and the chemicals around, which can then in some cases be extracted and processed to access the minerals themselves. In the Fell End clouds, for example, there is an old mine near to a large fold where the minerals malachite, azurite (both of which suggest the presence of usable copper ores), and galena can be found. Additionally, a lime kiln is present for decomposing limestone into quicklime. When this mine was in use during the Roman times, they could’ve potentially mined lead and copper.

This area has also been mined for its relatively accessible mineral supplies more recently. In the Lake District in Caldew Valley, there lies the Carrock Mine where ores of tungsten such as wolfram and scheelite have been mined. Mining was only thought viable here in certain instances – such as during both World Wars and the Korean War, when tungsten supplies were threatened.

Almost all rocks present are ancient – yet this is still a changing landscape. An ice age occurred ~16,000 years ago during the Pleistocene and the effects of this can be read in the landscape in certain places in the Dales where glaciations occurred.

Cautley Holme Beck. Red shows the scree, purple shows hummocky bedding and drumlins. Dark blue shows current current flow, light blue shows potential paleo current.
View from Cautley Waterfall. Purple shows bracken, pink shows drumlins, red line shows potential limit of glacier.

In the Cautley Holme Beck, a glaciation occurred. From reading the landscape, it is likely that the glacier started in the top area of the hill (the left most purple on the first image, with hummocky bedding; This is to the far right of the second image.). It then crept down through the valley, towards Low Haygarth, scraping the ground as it moved. It likely advanced only to the red line, which we can infer because this is where the bracken ends; Bracken prefers well drained soil, and after the glacier melts and retreats the escaping water would likely have created drainage paths throughout, allowing bracken to grow. As it retreated, collected rocks and debris within the ice were dumped out forming drumlins of till (as seen in the second photo), and later hummocky bedding around where the glaciation began.

The retreat of the glacier likely also meant that outcrop was exposed unsupported on the base. Once it was gone, this rock fell to produce scree slopes – hence, these scree slopes are only found on the outside path of the glacier and not on the inside.

The glacier, and others, potentially also affected the path of the feeder river. Originally this likely came through the far shallower V shaped valley heading to the north, however this now has very little water flow, with a waterfall  instead forming. The presence of a waterfall in this area like this suggests it is a new feature which has not eroded properly, which supports this hypothesis.

Cautley Falls

Once the glaciers had retreated the area was able to be colonized by humans. In one area, Victoria Cave has been foundd which contains an 11,000 year old harpoon point in a reindeer skeleton suggesting people have lived in the area for at least this long. Since that time a lot has changed.

Farming has taken a massive hold of the area. This has almost completely transformed the fauna and flora in the area, as without the millenia of farming that have occurred it would likely be covered almost entirely by woodland. Farming has driven grey wolves out from the area, which are now extinct here, while bear baiting has removed bears from Britain. This story is repeated again and again, so that todays Yorkshire Dales are almost entirely grass, bog, bracken and sheep.

Even today this sort of activity continues. Up until 2005 fox hunting was legal, and in some places this still occurs; When we visited the Yorkshire Dales on a mapping project, we saw a fox chased by a large pack of dogs through trees. Unfortunately, as we found out, the police in the area are unwilling to do anything without video or photo containing both the fox and the dogs – which is understandably needed as evidence, yet disappointing (to be clear, I have no issue with the police’s requirement for this).

Nowadays, the Yorkshire Dales are a point of pride for the beauty they present. The landscape is akin to a book, just waiting to be read. Millions of tourists visit the area year on year to go walking, hiking, running and mountain biking, and it is likely this will continue.