I have just completed my first semester of college and these things have been on my mind as I reflect.
1. You interact almost exclusively with people your own age.
You live with them, you hang out with them, you study with them -- even when you need to deal with something serious, you're often talking to someone no more than a few years older. I love this because we're all in the same boat and figuring things out together.
2. Professors might take an interest in you
If you stand out from the crowd professors will notice and now this actually matters. You can get papers published, get jobs, and other cool opportunities from impressing a professor. Perhaps this is more likely at a small school like Hamline, but it can and does happen anywhere.
3. You make so many decisions on your own
Day to day decisions of course, and bigger decisions such as what classes you're taking and what you plan to major in. The freedom is both exciting and relaxing.
4. Weekdays are fun
This was probably the biggest thing for me. I'm not actually in class for very much time, and all my classes are fairly spread out. In between classes and after classes I get to hang out with friends and we almost always do our homework together. In high school I really lived from weekend to weekend, but in college the week is fun in and of itself.
5. Weekends are even better
Going out is great, but my favorite part of the weekend is brunch on Saturday and Sunday morning with the squad, trying to piece together exactly what happened the night before. We've sat in our cafeteria for up to three hours, waiting for friends to arrive and bring their own piece of the story.
6. It's a fresh start
While the concept of a fresh start is somewhat deceiving, there are ways that you can take advantage of it. It isn't feasible or even wise to change yourself completely, but it's a good idea to think about how you want to be perceived. It's also really easy to be out if you weren't able to be out in high school. That's something I and friends of mine have really enjoyed. Meeting a lot of new people also means that you can tell all your best stories again. But don't be frustrated if you end up being sort of the same as you were before -- the real you will probably be appreciated more now.
Saturday, December 27, 2014
Tuesday, December 16, 2014
My Linguistics Research Paper: Atkinson's Theory of Phonemic Diversity
This is the research paper I wrote for my final project for my first semester Linguistics class. I chose this topic after seeing a post about Atkinson's theory on tumblr, and decided to look into it more. I've added some pictures and otherwise blog-ified this paper, as I usually do with academic papers published here.
In 2011 Quentin Atkinson, a psychology professor at the University of Auckland, sparked debate in the linguistics community with a study published in Science called “Phonemic Diversity Supports a Serial Founder Effect Model of Language Expansion from Africa.” The basis of this theory is that all human languages are descended from a single African language or a small collection of closely related African languages. His primary evidence for this is the degree of phonemic diversity of languages around the world. After analyzing 504 languages, Atkinson found that languages farther from Africa have fewer phonemes. This theory caught the attention of many popular news sources such as the New York Times and the Global Post, and was often presented as factual. However, many linguists published responses Atkinson’s hypothesis, calling out discrepancies in his argument.
A founder effect in genetics occurs because a smaller group of people naturally has a smaller range of genetic diversity. Around the world it is seen that there is less genetic diversity farther from Africa. This was used as support for the out-of-Africa model of human expansion around the world, with Oceania and South America among the last places to be populated by modern humans. Atkinson applied the concept of a founder effect to linguistics, with phonemic diversity analogue to genetic diversity. Many linguists think that this comparison is unfounded. Ian Maddieson, a linguist at UC Berkeley, wrote in a response to Atkinson that “a subgroup of speakers of a given language does not use a subset of the phonemes, but all of them.” To lose a phoneme completely due to segmentation of a population is unlikely, and would require all the words containing that phoneme to be lost as well. There are processes by which phonemes are lost and gained, but a founder effect alone does not account for these changes. Claire Bowern, a linguist at Yale, also responded to Atkinson’s study, saying that “founder effects in genetics are robust because of the time it takes for genetic diversity to recover after a bottleneck. Linguistic change is much more rapid.” She further invalidates this comparison by explaining that genetic diversity is affected by factors other than founder effects. Any significant population loss, such as plague or famine, has caused loss in genetic diversity, but no observed linguistic changes.
Atkinson defines phonemes as the “perceptually distinct units of sound that differentiate words." While a phoneme inventory doesn’t represent how many different sounds are actually used in a language (allophones), it shows which sounds speakers think of as distinct. Atkinson used the data in the World atlas of linguistic structures (WALS) to compare number of phonemes in 504 world languages, finding that African languages have the highest phonemic diversity. In his article, Maddieson shed some light on how phonemes were counted in WALS and the process was not totally accurate. For example, only basic vowel qualities were considered, and factors like length and nasalization were not accounted for, even though these create distinguishable phonemes in many languages. This means that the data Atkinson used in his study is not representative of how some languages actually function, and underestimated how many phonemes some languages have.
Furthermore, the number of phonemes doesn’t tell us as much about a language’s complexity than phonotactic rules and possible number of syllables. In his analysis, Atkinson uses some aspects of phoneme inventory size and some aspects of phonological possibilities to determine what he labels as “phonemic diversity” — and it’s not entirely clear what this measure is. Maddieson argues that the content of a language’s phonemic inventory should be taken into account as well as its actual size. Some sounds are rarer than others; a larger inventory isn’t necessarily more “diverse” than a smaller inventory. Bowern also questions what exactly Atkinson means by “phonemic diversity.” She believes that founder effects could lead to “sub-phonemic variation” — that is, at the level of the allophone — but not the overall size of phoneme inventories. A small splintered-off group of speakers could conceivably change the ways a phoneme is actually articulated, but this would be classified as phonetic change linguistically, and would not affect the number of phonemes in a language.
The basis of Atkinson’s hypothesis lies in the correlation between group size and phoneme inventory: “small populations have fewer phonemes.” He expands this to conclude that phonemes “are more likely to be lost in small founder populations.” If this is true, it makes sense that African languages would have the most phonemes, since human life is accepted to have started there. Then as humans spread out phonemes were lost, leading to fewer phonemes at the end of the migration track in places like Oceania and South America. While phonemes are always being lost and gained in languages, there doesn’t seem to be any reason for a founder effect to reduce the phoneme inventory. Atkinson also claimed that “contact and borrowing between groups of speakers” was a primary source of phoneme gain. Don Ringe, a linguistics professor at the University of Pennsylvania, analyzed phoneme loss and gain in Indo-European languages in response to Atkinson’s theory. He had several findings that call Atkinson’s work into question. For one he found that “phoneme loss does not greatly outpace phoneme creation.” With this in mind, it seems unlikely that so many phonemes would be lost as humans migrated out of Africa. Additionally, Ringe found that “most of the new phonemes” in the Indo-European family “arose by language-internal processes; only 8% were acquired by borrowing.” Ringe concludes that “the Oceanic reduction of phoneme inventories is a result of internal factors,” specifically the phonological rules of such languages, “not the lack of language contact.” This directly contradicts Atkinson’s theory and its underlying assumption that more phonemes will be lost than gained over time if small populations are isolated. It seems there may be another factor at work here to explain the correlation between small population and fewer phonemes, but it’s clear that the first doesn’t lead to the second.
Ringe also points out that population size is almost irrelevant at the time in history when humans began leaving Africa: “no language could have had more than about 100,000 speakers at most." Even an “origin” language would not have had enough speakers to make a significant difference in size between the main population and fragmented founder groups. Östen Dahl, a linguist at Stockholm University, notes in his response to Atkinson that only size of phoneme inventory correlates with population; there is no decrease in complexity of the language with regard to morphology or syntax for instance. In fact, languages with fewer speakers often “have greater complexity of at least certain aspects of grammar." This suggests that languages do not “simplify” in smaller populations, and equating size of phoneme inventory with complexity is not a fair judgment.
Finally, a lot of problems with Atkinson’s study arise from the data he worked with and how he analyzed it. The 504 languages examined constitute only 5% of languages still spoken today. Furthermore, these are all modern languages; there is no reason to think that our current language distribution is comparable to what the earth was like during the first human expansions. Bowern raises the point that “all the largest language families in the present world are the result of expansions in the Holocene period,” which spans from about 10,000 years ago to today. Humans are thought to have left Africa long before the Holocene period, with current estimates ranging from 40,000 to 70,000 years ago.
In addition to Atkinson’s dataset being unrepresentative of the environment being studied, it is small and incomplete. Vladimir Pericliev, a Bulgarian linguist, points out that different patterns could have easily emerged from different data, more complete data, or different analysis techniques. Atkinson may have interpreted the data from the point of view of someone with the pre-existing knowledge that human life began in Africa. Pericliev demonstrates an alternative interpretation in his response: If we instead look at phonemic complexity from the perspective of child language acquisition, from generation to generation, we would arrive at the opposite conclusion — that language originated in Oceania and South America and grew more complex as humans migrated toward Africa. Of course this is ridiculous as we know scientifically that humans migrated in the opposite direction, but Pericliev was able to expose the ambiguity in the data through this example.
The origin of language has been a topic of speculation for centuries. Although Atkinson’s theory fits with our current understanding of early human migration patterns, there are numerous problems with his data and analysis. Several linguists have responded to his study, pointing out: the unwarranted analogy of founder effects in genetics to linguistics; the inconsistent definition of phonemes and phonemic diversity; the missing link between size of population and phoneme inventory; and other issues. Despite this, there is undoubtedly a lot to be learned by comparing language evolution to early human migration. We may not have enough data on early languages to come to a definitive conclusion, but this is a subject worth exploring.
Sources:
Atkinson, Quentin D. “Phonemic Diversity Supports a Serial Founder Effect Model of Language Expansion from Africa.” Science 15 (2011): 346-9. ScienceMag. Web. 8 Dec. 2014.
Bowern, Claire. "Out of Africa? the Logic of Phoneme Inventories and Founder Effects." Linguistic Typology 15.2 (2011): 207-16. ProQuest. Web. 8 Dec. 2014.
Dahl, Östen. "Are Small Languages More Or Less Complex than Big Ones?" Linguistic Typology 15.2 (2011): 171-5. ProQuest. Web. 8 Dec. 2014.
Maddieson, Ian, et al. "Geographical Distribution of Phonological Complexity." Linguistic Typology 15.2 (2011): 267-79. ProQuest. Web. 8 Dec. 2014.
Pericliev, Vladimir. "On Phonemic Diversity and the Origin of Language in Africa." Linguistic Typology 15.2 (2011): 217-21. ProQuest. Web. 8 Dec. 2014.
Ringe, Don. "A Pilot Study for an Investigation into Atkinson's Hypothesis." Linguistic Typology 15.2 (2011): 223-31. ProQuest. Web. 8 Dec. 2014.
In 2011 Quentin Atkinson, a psychology professor at the University of Auckland, sparked debate in the linguistics community with a study published in Science called “Phonemic Diversity Supports a Serial Founder Effect Model of Language Expansion from Africa.” The basis of this theory is that all human languages are descended from a single African language or a small collection of closely related African languages. His primary evidence for this is the degree of phonemic diversity of languages around the world. After analyzing 504 languages, Atkinson found that languages farther from Africa have fewer phonemes. This theory caught the attention of many popular news sources such as the New York Times and the Global Post, and was often presented as factual. However, many linguists published responses Atkinson’s hypothesis, calling out discrepancies in his argument.
A founder effect in genetics occurs because a smaller group of people naturally has a smaller range of genetic diversity. Around the world it is seen that there is less genetic diversity farther from Africa. This was used as support for the out-of-Africa model of human expansion around the world, with Oceania and South America among the last places to be populated by modern humans. Atkinson applied the concept of a founder effect to linguistics, with phonemic diversity analogue to genetic diversity. Many linguists think that this comparison is unfounded. Ian Maddieson, a linguist at UC Berkeley, wrote in a response to Atkinson that “a subgroup of speakers of a given language does not use a subset of the phonemes, but all of them.” To lose a phoneme completely due to segmentation of a population is unlikely, and would require all the words containing that phoneme to be lost as well. There are processes by which phonemes are lost and gained, but a founder effect alone does not account for these changes. Claire Bowern, a linguist at Yale, also responded to Atkinson’s study, saying that “founder effects in genetics are robust because of the time it takes for genetic diversity to recover after a bottleneck. Linguistic change is much more rapid.” She further invalidates this comparison by explaining that genetic diversity is affected by factors other than founder effects. Any significant population loss, such as plague or famine, has caused loss in genetic diversity, but no observed linguistic changes.
Atkinson defines phonemes as the “perceptually distinct units of sound that differentiate words." While a phoneme inventory doesn’t represent how many different sounds are actually used in a language (allophones), it shows which sounds speakers think of as distinct. Atkinson used the data in the World atlas of linguistic structures (WALS) to compare number of phonemes in 504 world languages, finding that African languages have the highest phonemic diversity. In his article, Maddieson shed some light on how phonemes were counted in WALS and the process was not totally accurate. For example, only basic vowel qualities were considered, and factors like length and nasalization were not accounted for, even though these create distinguishable phonemes in many languages. This means that the data Atkinson used in his study is not representative of how some languages actually function, and underestimated how many phonemes some languages have.
Furthermore, the number of phonemes doesn’t tell us as much about a language’s complexity than phonotactic rules and possible number of syllables. In his analysis, Atkinson uses some aspects of phoneme inventory size and some aspects of phonological possibilities to determine what he labels as “phonemic diversity” — and it’s not entirely clear what this measure is. Maddieson argues that the content of a language’s phonemic inventory should be taken into account as well as its actual size. Some sounds are rarer than others; a larger inventory isn’t necessarily more “diverse” than a smaller inventory. Bowern also questions what exactly Atkinson means by “phonemic diversity.” She believes that founder effects could lead to “sub-phonemic variation” — that is, at the level of the allophone — but not the overall size of phoneme inventories. A small splintered-off group of speakers could conceivably change the ways a phoneme is actually articulated, but this would be classified as phonetic change linguistically, and would not affect the number of phonemes in a language.
The basis of Atkinson’s hypothesis lies in the correlation between group size and phoneme inventory: “small populations have fewer phonemes.” He expands this to conclude that phonemes “are more likely to be lost in small founder populations.” If this is true, it makes sense that African languages would have the most phonemes, since human life is accepted to have started there. Then as humans spread out phonemes were lost, leading to fewer phonemes at the end of the migration track in places like Oceania and South America. While phonemes are always being lost and gained in languages, there doesn’t seem to be any reason for a founder effect to reduce the phoneme inventory. Atkinson also claimed that “contact and borrowing between groups of speakers” was a primary source of phoneme gain. Don Ringe, a linguistics professor at the University of Pennsylvania, analyzed phoneme loss and gain in Indo-European languages in response to Atkinson’s theory. He had several findings that call Atkinson’s work into question. For one he found that “phoneme loss does not greatly outpace phoneme creation.” With this in mind, it seems unlikely that so many phonemes would be lost as humans migrated out of Africa. Additionally, Ringe found that “most of the new phonemes” in the Indo-European family “arose by language-internal processes; only 8% were acquired by borrowing.” Ringe concludes that “the Oceanic reduction of phoneme inventories is a result of internal factors,” specifically the phonological rules of such languages, “not the lack of language contact.” This directly contradicts Atkinson’s theory and its underlying assumption that more phonemes will be lost than gained over time if small populations are isolated. It seems there may be another factor at work here to explain the correlation between small population and fewer phonemes, but it’s clear that the first doesn’t lead to the second.
Ringe also points out that population size is almost irrelevant at the time in history when humans began leaving Africa: “no language could have had more than about 100,000 speakers at most." Even an “origin” language would not have had enough speakers to make a significant difference in size between the main population and fragmented founder groups. Östen Dahl, a linguist at Stockholm University, notes in his response to Atkinson that only size of phoneme inventory correlates with population; there is no decrease in complexity of the language with regard to morphology or syntax for instance. In fact, languages with fewer speakers often “have greater complexity of at least certain aspects of grammar." This suggests that languages do not “simplify” in smaller populations, and equating size of phoneme inventory with complexity is not a fair judgment.
Finally, a lot of problems with Atkinson’s study arise from the data he worked with and how he analyzed it. The 504 languages examined constitute only 5% of languages still spoken today. Furthermore, these are all modern languages; there is no reason to think that our current language distribution is comparable to what the earth was like during the first human expansions. Bowern raises the point that “all the largest language families in the present world are the result of expansions in the Holocene period,” which spans from about 10,000 years ago to today. Humans are thought to have left Africa long before the Holocene period, with current estimates ranging from 40,000 to 70,000 years ago.
In addition to Atkinson’s dataset being unrepresentative of the environment being studied, it is small and incomplete. Vladimir Pericliev, a Bulgarian linguist, points out that different patterns could have easily emerged from different data, more complete data, or different analysis techniques. Atkinson may have interpreted the data from the point of view of someone with the pre-existing knowledge that human life began in Africa. Pericliev demonstrates an alternative interpretation in his response: If we instead look at phonemic complexity from the perspective of child language acquisition, from generation to generation, we would arrive at the opposite conclusion — that language originated in Oceania and South America and grew more complex as humans migrated toward Africa. Of course this is ridiculous as we know scientifically that humans migrated in the opposite direction, but Pericliev was able to expose the ambiguity in the data through this example.
The origin of language has been a topic of speculation for centuries. Although Atkinson’s theory fits with our current understanding of early human migration patterns, there are numerous problems with his data and analysis. Several linguists have responded to his study, pointing out: the unwarranted analogy of founder effects in genetics to linguistics; the inconsistent definition of phonemes and phonemic diversity; the missing link between size of population and phoneme inventory; and other issues. Despite this, there is undoubtedly a lot to be learned by comparing language evolution to early human migration. We may not have enough data on early languages to come to a definitive conclusion, but this is a subject worth exploring.
Sources:
Atkinson, Quentin D. “Phonemic Diversity Supports a Serial Founder Effect Model of Language Expansion from Africa.” Science 15 (2011): 346-9. ScienceMag. Web. 8 Dec. 2014.
Bowern, Claire. "Out of Africa? the Logic of Phoneme Inventories and Founder Effects." Linguistic Typology 15.2 (2011): 207-16. ProQuest. Web. 8 Dec. 2014.
Dahl, Östen. "Are Small Languages More Or Less Complex than Big Ones?" Linguistic Typology 15.2 (2011): 171-5. ProQuest. Web. 8 Dec. 2014.
Maddieson, Ian, et al. "Geographical Distribution of Phonological Complexity." Linguistic Typology 15.2 (2011): 267-79. ProQuest. Web. 8 Dec. 2014.
Pericliev, Vladimir. "On Phonemic Diversity and the Origin of Language in Africa." Linguistic Typology 15.2 (2011): 217-21. ProQuest. Web. 8 Dec. 2014.
Ringe, Don. "A Pilot Study for an Investigation into Atkinson's Hypothesis." Linguistic Typology 15.2 (2011): 223-31. ProQuest. Web. 8 Dec. 2014.
Fictional friend groups to compare your real life squad to
If you're in a close-knit friend group (or "squad") like I am, you've probably had the experience of comparing your friends to a famous fictional friend group. Furthermore, you've probably noticed that there are basic character types in fiction and real life that lead to a functioning group. Your friend group is probably right around four people, since that's demonstrably the best size -- and looking at the following squads, these numbers repeat often.
I should write my thesis about squad makeup. Squadology.
Anyway, here's your resource for coming up with group Halloween costumes, or just fun conversation. Keep the members of your squad in mind. It will probably be immediately apparent who's who.You can add in other characters or combine characters into an amalgam if you need to in order to fit your own squad.
I should write my thesis about squad makeup. Squadology.
Anyway, here's your resource for coming up with group Halloween costumes, or just fun conversation. Keep the members of your squad in mind. It will probably be immediately apparent who's who.You can add in other characters or combine characters into an amalgam if you need to in order to fit your own squad.
Ninja Turtles
 |
| Leonardo, Raphael, Donatello and Michelangelo. |
Winnie the Pooh
 |
| Tigger, Pooh, Eeyore and Piglet. |
Golden Girls
 |
| Rose, Dorothy, Blanche and Sophia. |
Mean Girls
 |
| Cady, Regina, Karen and Gretchen. |
Wizard of Oz
 |
| Dorothy, the Scarecrow, the Tin Man and the Cowardly Lion. |
How I Met Your Mother
 |
| Barney, Ted, Robin, Marshall and Lily. |
PowerPuff Girls
 |
| Blossom, Bubbles and Buttercup. |
Sonic the Hedgehog
 |
| Sonic, Knuckles and Tails. |
F.R.I.E.N.D.S.
 |
| Joey, Ross, Chandler, Monica, Rachel and Phoebe. |
Monday, December 1, 2014
The Fault in Our Faults: Volcanism in the North Atlantic
(This is the research paper I wrote for this semester in my English class. We could research basically anything we wanted, and I genuinely wanted to know more about volcanism in Iceland -- which led me to discover a lot about volcanism in general, and the geology of the entire North Atlantic. I've added pictures and otherwise blog-icized this paper for your entertainment, but the language of the paper remains unchanged. Also, credit to my friend Nick for coming up with the clever title.)
The Mid-Atlantic Ridge is the divergent boundary that runs nearly the entire distance from the north pole to the south pole. As a slow spreading ridge, two plates move apart, causing the Atlantic Ocean to widen at a rate of about 2.5 cm per year. This has created the longest mountain range on Earth. Of course, the vast majority of this range is underwater. There are several islands near the ridge, but the only landform to exist directly on top of it is Iceland. Iceland is a hotspot of volcanic activity, with about 130 active and inactive volcanoes, and 30 active volcanic systems altogether.
According to the Guide to Iceland tourism website, this volcanism is due to its location along the Mid-Atlantic Ridge [1]. This certainly makes sense since “most volcanoes on earth are a result of plate tectonics” [2]. A map of all the volcanoes in the world reveals that the vast majority are along plate boundaries, with the rim of the Pacific plate so active to earn itself the nickname “Ring of Fire.” But the Mid-Atlantic is much quieter in comparison; Iceland is one of only two “hotspots” of volcanic activity along the ridge. So contrary to what many internet sources report, volcanism in Iceland cannot be attributed solely to its location on the Mid-Atlantic Ridge.
The other hotspot along the Mid-Atlantic Ridge is the archipelago of the Azores Islands. The Azores are a chain of nine volcanic islands that together constitute an autonomous region of Portugal, and are located about 850 miles off the coast of mainland Portugal. They lie around the “triple junction among the Eurasian, Nubian, and North American plates" [3]. This means that the Azores are along both the divergent Mid-Atlantic Ridge and the transform fault between the Eurasian and African (or Nubian) plates. This creates a different environment of tectonic activity than is seen in Iceland. However, the plate boundary may not be responsible for volcanic activity in the Azores either.
Hotspots, or regions with a high level of volcanic activity, “are not necessarily associated with a plate boundary,” according to Berkeley geochemistry professor, Donald DePaolo [2]. The hotspot of Hawaii for instance — one of the most volcanically active places in the world — is in the middle of the Pacific plate, thousands of miles from a fault line. The same is true of Yellowstone, which is near the center of the North American plate. Even the Iceland hotspot can’t seem to be explained by the presence of a plate boundary; if the Mid-Atlantic Ridge is responsible for Iceland’s volcanism, it would logically follow that the rest of the ridge be equally active. But the only active volcanoes along the Mid-Atlantic are in the isolated and concentrated hotspots of Iceland and the Azores.
In 1971, Princeton geology professor W. Jason Morgan proposed the existence of plumes caused by “convection in the lower mantle” as an explanation for hotspots around the world [4]. Mantle plumes are described as “hot, buoyant upwelling regions beneath the Earth’s lithosphere” [5]. Plumes are thought to act independently from plate tectonics since they originate so deep within the Earth, at the boundary between the core and the mantle, almost two thousand miles beneath the surface of the Earth. This means that plates and ridges — the crust — can move around without affecting the mostly stationary hotspots [2]. The clearest example of this in action is Hawaii. The plume underneath the Hawaiian hotspot has stayed in the same spot while the Pacific plate has migrated, creating a chain of islands 1,500 miles long.
It hasn’t been proven that mantle plumes exist, nor that they cause volcanic activity, but there’s strong evidence for a plume existing underneath Iceland. Morgan initially modeled that there were twenty deep mantle plumes around the world. One piece of evidence he used to justify this claim was a world gravity map made by William M. Kaula, a professor at the University of California, Los Angeles. Kaula’s map showed “gravity highs over Iceland, Hawaii, and most of the other hotspots” [4]. These gravity highs are thought to be evidence of a large swelling plume in the Earth’s mantle.
One indication of a gravity high for plumes under oceanic plates is the depth of the ocean. Hotspots often exist around “abnormally shallow parts of the ocean” [4]. “The Azores are located on a shallow plateau” toward the middle of the Atlantic Ocean, which points to the existence of a mantle plume [3]. The water around Iceland as well is significantly shallower than the usual depth of the North Atlantic [4].
There is also seismic evidence of a plume at the core-mantle boundary beneath Iceland. Donald V. Helmberger and Lianxing Wen of the Seismological Laboratory at the California Institute of Technology used seismic waves to model the Iceland plume in 1998. Seismic waves are caused by movement within the earth, whether that be earthquakes, explosions or volcanoes. This research was conducted to determine whether the plume under Iceland, at this point widely accepted to be true, exists at the “core-mantle boundary or at the base of the upper mantle” [6]. The researchers’ conclusion was that the plume originated very deep within the earth, at the core-mantle boundary.
Though not all hotspots appear to be caused by mantle plumes. The Yellowstone hotspot, which can’t be explained by a plate boundary, has yielded no seismological evidence for a lower mantle plume [2]. Furthermore, not all mantle plumes are created equally. Kaula’s gravity map reveals the differences in strength between hotspots through variation in “the magnitude of the gravity” [4]. In a similar way, Bernard Bourdon of the European Association of Geochemistry characterizes the strength of hotspots based on their “buoyancy flux and mantle temperature.” This essentially measures how much heat the mantle plume brings from the deep mantle to the upper mantle. Stronger plumes have higher temperatures and are high buoyancy flux. Since Iceland and the Azores have “lower excess temperatures” and are low buoyancy flux, they are considered weaker hotspots in comparison to the very strong hotspot of Hawaii [5].
According to Norman Sleep, professor of Geophysics at Stanford University, the Iceland plume has only “1/6 of the volume flux of Hawaii” and the Azores hotspot is even smaller and weaker. So, if these plumes weren’t positioned under the divergent Mid-Atlantic ridge, or another equally weak crustal spot, they would not be nearly as volcanic [7]. The strength of the Hawaii hotspot allows it to break through the thick and fast-moving Pacific plate, but a weaker plume would not produce as much volcanism.
Even though Iceland and the Azores have weaker plumes, the two are still highly volcanic. Iceland in particular is among the world’s most volcanically active places, considered one of the two most “prominent hotspots” along with Hawaii [7]. So the full explanation of Iceland’s volcanism is most likely due to a combination of the mantle plume and the Mid-Atlantic Ridge, and the interactions between the two. In Iceland, tectonic and plume activity come together to cause magmatism at the surface, along the rift. There are several fractures in and around Iceland. The Mid-Atlantic Ridge, of course, cuts right through the landform (called the Reykjanes Ridge where it’s above ground), and there is another main off-shoot to the south of the island. All the active volcanoes in Iceland lie right in and around the fault lines regardless of the size and scope of the underlying plume.
The volcanism in the Azores has a similar story, caused by a “mantle plume interacting with the Mid-Atlantic Ridge,” according to Daniele Trippanera, a Ph.D. student in the geology department at Roma Tre University [3]. The Azores differs slightly from Iceland, though, due to the presence of a transform fault between the Eurasian and African plates. Transform plate boundaries, where two plates move past each other, are usually not associated with volcanic activity.
A mantle plume can’t cause magmatism on its own. Cracks in the plate, whether at plate boundaries or in the middle of a plate, are “necessary for plume magma to ascend." Iceland and the Azores both have an obvious co-existence of plumes and faults, but “plate cracking is evident along the Hawaiian chain” as well [7].
In the case of Hawaii it makes sense that the strong upwelling mantle plume broke through the Pacific plate to cause these cracks in the crust. But looking at Iceland and the Azores, do plumes and plate boundaries have any causal relationship to each other? R.I Hill, a professor at Australian National University, writes that plumes and plate tectonics are caused by “two distinct modes of convection” in the mantle, and “operate largely independently” [8]. Craig Parkin, a professor at Cambridge University, takes a similar stance, referring to the conjunction of plate boundary and plume a “coincidence” [9].
Morgan, on the other hand, believes that plumes can lead to “continental break-up” especially in the case of the North Atlantic. He proposed that the Iceland and Azores plumes created “currents in the asthenosphere” that broke through the ocean crust and led to the spreading of the Atlantic Ocean. He points to the prevalence of mantle plumes at triple junctions, such as the Azores and the Galapagos, as evidence that plumes can create plate boundaries [4]. Kevin Burke, professor of geology at University College London, also believes that the relationship between triple junctions illustrate how plumes affect tectonic activity. In his 1973 article, “Plume-Generated Triple-Junctions,” Burke hypothesized that plate boundaries and rifts initially develop because of plumes, an idea that Morgan briefly mentioned in his article two years earlier [10]. Looking at how many plumes exist along plate boundaries, especially triple junctions, it does seem that these two forces are related.
The commonly found explanation for volcanic activity in Iceland centers on its location on top of the Mid-Atlantic Ridge. If it were as simple as that one would expect to find volcanic hotspots and continental growth all along the ridge, but in reality there is only volcanism in two isolated places in the Mid-Atlantic: Iceland and the Azores. During the past few decades there has been a lot of debate about the existence of mantle plumes and how they behave.
The full explanation of volcanism in Iceland is complicated, and combines the effect of both a relatively weak plume at the core-mantle boundary and the spreading center of the Mid-Atlantic Ridge. These two factors, however, may not have occurred in a mere coincidence. It’s likely that the plumes in both Iceland and the Azores played a part in creating the ridge in the North Atlantic, leading to the spreading of the Atlantic Ocean. In turn, the ridge in Iceland magnified the effect of the plume, making it one of the world’s most notable volcanic hotspots.
References:
1: Guide to Iceland website: "Volcanoes in Iceland"
2: "Deep Origin Of Hotspots -- The Mantle Plume Model." Donald J. DePaolo and Michael Manga.
3: "Relationships Between Tectonics And Magmatism In A Transtensive/ Transform Setting: An Example From Faial Island (Azores, Portugal)." Daniele Trippanera, et al.
4: "Convection Plumes in the Lower Mantle." W. Jason Morgan.
5: "Insights Into The Dynamics Of Mantle Plumes From Uranium-Series Geochemistry." Bernard Bourdon, et al.
6: "Seismic Evidence That The Source Of The Iceland Hotspot Lies At The Core-Mantle Boundary." D.V. Helmberger and L. Wen.
7: "Origins of the Plume Hypothesis and Some of Its Implications." Norman H. Sleep.
8: "Mantle plumes and continental tectonics." R.I. Hill, et al.
9: "Imaging The Pulsing Iceland Mantle Plume Through The Eocene." Craig Parkin, et al.
10: "Plume-Generated Triple Junctions: Key Indicators in Applying Plate Tectonics to Old Rocks." Kevin Burke and J.F. Dewey.
The Mid-Atlantic Ridge is the divergent boundary that runs nearly the entire distance from the north pole to the south pole. As a slow spreading ridge, two plates move apart, causing the Atlantic Ocean to widen at a rate of about 2.5 cm per year. This has created the longest mountain range on Earth. Of course, the vast majority of this range is underwater. There are several islands near the ridge, but the only landform to exist directly on top of it is Iceland. Iceland is a hotspot of volcanic activity, with about 130 active and inactive volcanoes, and 30 active volcanic systems altogether.
According to the Guide to Iceland tourism website, this volcanism is due to its location along the Mid-Atlantic Ridge [1]. This certainly makes sense since “most volcanoes on earth are a result of plate tectonics” [2]. A map of all the volcanoes in the world reveals that the vast majority are along plate boundaries, with the rim of the Pacific plate so active to earn itself the nickname “Ring of Fire.” But the Mid-Atlantic is much quieter in comparison; Iceland is one of only two “hotspots” of volcanic activity along the ridge. So contrary to what many internet sources report, volcanism in Iceland cannot be attributed solely to its location on the Mid-Atlantic Ridge.
The other hotspot along the Mid-Atlantic Ridge is the archipelago of the Azores Islands. The Azores are a chain of nine volcanic islands that together constitute an autonomous region of Portugal, and are located about 850 miles off the coast of mainland Portugal. They lie around the “triple junction among the Eurasian, Nubian, and North American plates" [3]. This means that the Azores are along both the divergent Mid-Atlantic Ridge and the transform fault between the Eurasian and African (or Nubian) plates. This creates a different environment of tectonic activity than is seen in Iceland. However, the plate boundary may not be responsible for volcanic activity in the Azores either.
Hotspots, or regions with a high level of volcanic activity, “are not necessarily associated with a plate boundary,” according to Berkeley geochemistry professor, Donald DePaolo [2]. The hotspot of Hawaii for instance — one of the most volcanically active places in the world — is in the middle of the Pacific plate, thousands of miles from a fault line. The same is true of Yellowstone, which is near the center of the North American plate. Even the Iceland hotspot can’t seem to be explained by the presence of a plate boundary; if the Mid-Atlantic Ridge is responsible for Iceland’s volcanism, it would logically follow that the rest of the ridge be equally active. But the only active volcanoes along the Mid-Atlantic are in the isolated and concentrated hotspots of Iceland and the Azores.
In 1971, Princeton geology professor W. Jason Morgan proposed the existence of plumes caused by “convection in the lower mantle” as an explanation for hotspots around the world [4]. Mantle plumes are described as “hot, buoyant upwelling regions beneath the Earth’s lithosphere” [5]. Plumes are thought to act independently from plate tectonics since they originate so deep within the Earth, at the boundary between the core and the mantle, almost two thousand miles beneath the surface of the Earth. This means that plates and ridges — the crust — can move around without affecting the mostly stationary hotspots [2]. The clearest example of this in action is Hawaii. The plume underneath the Hawaiian hotspot has stayed in the same spot while the Pacific plate has migrated, creating a chain of islands 1,500 miles long.
It hasn’t been proven that mantle plumes exist, nor that they cause volcanic activity, but there’s strong evidence for a plume existing underneath Iceland. Morgan initially modeled that there were twenty deep mantle plumes around the world. One piece of evidence he used to justify this claim was a world gravity map made by William M. Kaula, a professor at the University of California, Los Angeles. Kaula’s map showed “gravity highs over Iceland, Hawaii, and most of the other hotspots” [4]. These gravity highs are thought to be evidence of a large swelling plume in the Earth’s mantle.
One indication of a gravity high for plumes under oceanic plates is the depth of the ocean. Hotspots often exist around “abnormally shallow parts of the ocean” [4]. “The Azores are located on a shallow plateau” toward the middle of the Atlantic Ocean, which points to the existence of a mantle plume [3]. The water around Iceland as well is significantly shallower than the usual depth of the North Atlantic [4].
There is also seismic evidence of a plume at the core-mantle boundary beneath Iceland. Donald V. Helmberger and Lianxing Wen of the Seismological Laboratory at the California Institute of Technology used seismic waves to model the Iceland plume in 1998. Seismic waves are caused by movement within the earth, whether that be earthquakes, explosions or volcanoes. This research was conducted to determine whether the plume under Iceland, at this point widely accepted to be true, exists at the “core-mantle boundary or at the base of the upper mantle” [6]. The researchers’ conclusion was that the plume originated very deep within the earth, at the core-mantle boundary.
Though not all hotspots appear to be caused by mantle plumes. The Yellowstone hotspot, which can’t be explained by a plate boundary, has yielded no seismological evidence for a lower mantle plume [2]. Furthermore, not all mantle plumes are created equally. Kaula’s gravity map reveals the differences in strength between hotspots through variation in “the magnitude of the gravity” [4]. In a similar way, Bernard Bourdon of the European Association of Geochemistry characterizes the strength of hotspots based on their “buoyancy flux and mantle temperature.” This essentially measures how much heat the mantle plume brings from the deep mantle to the upper mantle. Stronger plumes have higher temperatures and are high buoyancy flux. Since Iceland and the Azores have “lower excess temperatures” and are low buoyancy flux, they are considered weaker hotspots in comparison to the very strong hotspot of Hawaii [5].
According to Norman Sleep, professor of Geophysics at Stanford University, the Iceland plume has only “1/6 of the volume flux of Hawaii” and the Azores hotspot is even smaller and weaker. So, if these plumes weren’t positioned under the divergent Mid-Atlantic ridge, or another equally weak crustal spot, they would not be nearly as volcanic [7]. The strength of the Hawaii hotspot allows it to break through the thick and fast-moving Pacific plate, but a weaker plume would not produce as much volcanism.
Even though Iceland and the Azores have weaker plumes, the two are still highly volcanic. Iceland in particular is among the world’s most volcanically active places, considered one of the two most “prominent hotspots” along with Hawaii [7]. So the full explanation of Iceland’s volcanism is most likely due to a combination of the mantle plume and the Mid-Atlantic Ridge, and the interactions between the two. In Iceland, tectonic and plume activity come together to cause magmatism at the surface, along the rift. There are several fractures in and around Iceland. The Mid-Atlantic Ridge, of course, cuts right through the landform (called the Reykjanes Ridge where it’s above ground), and there is another main off-shoot to the south of the island. All the active volcanoes in Iceland lie right in and around the fault lines regardless of the size and scope of the underlying plume.
The volcanism in the Azores has a similar story, caused by a “mantle plume interacting with the Mid-Atlantic Ridge,” according to Daniele Trippanera, a Ph.D. student in the geology department at Roma Tre University [3]. The Azores differs slightly from Iceland, though, due to the presence of a transform fault between the Eurasian and African plates. Transform plate boundaries, where two plates move past each other, are usually not associated with volcanic activity.
A mantle plume can’t cause magmatism on its own. Cracks in the plate, whether at plate boundaries or in the middle of a plate, are “necessary for plume magma to ascend." Iceland and the Azores both have an obvious co-existence of plumes and faults, but “plate cracking is evident along the Hawaiian chain” as well [7].
In the case of Hawaii it makes sense that the strong upwelling mantle plume broke through the Pacific plate to cause these cracks in the crust. But looking at Iceland and the Azores, do plumes and plate boundaries have any causal relationship to each other? R.I Hill, a professor at Australian National University, writes that plumes and plate tectonics are caused by “two distinct modes of convection” in the mantle, and “operate largely independently” [8]. Craig Parkin, a professor at Cambridge University, takes a similar stance, referring to the conjunction of plate boundary and plume a “coincidence” [9].
Morgan, on the other hand, believes that plumes can lead to “continental break-up” especially in the case of the North Atlantic. He proposed that the Iceland and Azores plumes created “currents in the asthenosphere” that broke through the ocean crust and led to the spreading of the Atlantic Ocean. He points to the prevalence of mantle plumes at triple junctions, such as the Azores and the Galapagos, as evidence that plumes can create plate boundaries [4]. Kevin Burke, professor of geology at University College London, also believes that the relationship between triple junctions illustrate how plumes affect tectonic activity. In his 1973 article, “Plume-Generated Triple-Junctions,” Burke hypothesized that plate boundaries and rifts initially develop because of plumes, an idea that Morgan briefly mentioned in his article two years earlier [10]. Looking at how many plumes exist along plate boundaries, especially triple junctions, it does seem that these two forces are related.
The commonly found explanation for volcanic activity in Iceland centers on its location on top of the Mid-Atlantic Ridge. If it were as simple as that one would expect to find volcanic hotspots and continental growth all along the ridge, but in reality there is only volcanism in two isolated places in the Mid-Atlantic: Iceland and the Azores. During the past few decades there has been a lot of debate about the existence of mantle plumes and how they behave.
The full explanation of volcanism in Iceland is complicated, and combines the effect of both a relatively weak plume at the core-mantle boundary and the spreading center of the Mid-Atlantic Ridge. These two factors, however, may not have occurred in a mere coincidence. It’s likely that the plumes in both Iceland and the Azores played a part in creating the ridge in the North Atlantic, leading to the spreading of the Atlantic Ocean. In turn, the ridge in Iceland magnified the effect of the plume, making it one of the world’s most notable volcanic hotspots.
References:
1: Guide to Iceland website: "Volcanoes in Iceland"
2: "Deep Origin Of Hotspots -- The Mantle Plume Model." Donald J. DePaolo and Michael Manga.
3: "Relationships Between Tectonics And Magmatism In A Transtensive/ Transform Setting: An Example From Faial Island (Azores, Portugal)." Daniele Trippanera, et al.
4: "Convection Plumes in the Lower Mantle." W. Jason Morgan.
5: "Insights Into The Dynamics Of Mantle Plumes From Uranium-Series Geochemistry." Bernard Bourdon, et al.
6: "Seismic Evidence That The Source Of The Iceland Hotspot Lies At The Core-Mantle Boundary." D.V. Helmberger and L. Wen.
7: "Origins of the Plume Hypothesis and Some of Its Implications." Norman H. Sleep.
8: "Mantle plumes and continental tectonics." R.I. Hill, et al.
9: "Imaging The Pulsing Iceland Mantle Plume Through The Eocene." Craig Parkin, et al.
10: "Plume-Generated Triple Junctions: Key Indicators in Applying Plate Tectonics to Old Rocks." Kevin Burke and J.F. Dewey.
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