Nature of Auckland’s Volcanoes * Eruption History Volcanoes are an important feature of the Auckland city landscape. In most cases they are emphasized by their different forms such as reserves and parks, while in the other locations, they have been quarried away to meet the city’s demand for construction material. According to research, distributed over a 20km radius are approximately about 49 volcanoes in the Auckland region, this area is referred to as the Auckland volcanic field.
The distribution of the volcanoes is as shown in the following figure Source: http://gns. cri. nz Page 1 0f 19 Majority of the volcanoes in Auckland are small coned and less than 150 meters in height. Most of these extinct volcanoes grew by eruptions, which lasted only for a few months or possibly a few years. In some cases, only a single cone resulted from the eruption but there is also proof that some eruptions have built several cones, forming multiple domes.
The type of volcanic activity which has created the Auckland volcanic field is referred to as the monogenetic which means that each time a volcanoe has erupted, it has occurred at a new location. Each of these eruptions is the result of a single batch of magma which rises from its source, the magma chamber in the mantle about 100km beneath the land. Source: http://gns. cri. nz The Auckland volcanic field from Mt Eden Page 2 of 19
However, this monogenetic nature of Auckland’s volcanic lanscape has particular concerns for volcanic hazards because in the event of an eruption, rather than one of the existing volcanoes becoming active, a new volcano is bound to erupt and settle over time in its dormant form. Because of this situation, a hazard map based on any of the locations cannot be drawn as the entire field has to be considered under the threat of a future volcanic eruption. Nature of Auckland’s Volcanoes
The Term Paper on Volcanoes Lava Volcano Volcanic
Volcanoes JACK KN OFF WR 327 Technical Report Spring '99 Introduction In this report I plan to discuss the geological event of volcanic eruptions and the disasters they cause. To me, this is a fascinating topic and timely seeing how the 19 th anniversary of the eruption of Mt. St. Helens is upon us. I hope to inform people of the mass destruction that is caused by the eruption of a volcano. The ...
The Auckland volcanic field originates to the presence of a region of hot rock known as a hot spot or plume located approximately 100km beneath the field. In this hot spot, temperatures get high enough so that the rock begins to melt. When a certain amount of molten rock has accumulated, it separates itself from the solid component and rises towards the surface. This melted rock is known as basalt magma and one of its most important characteristics is that it has a very low viscosity, meaning the thickness of the substance is low causing it to be runny. This causes it to force its way through the upper crust quite quickly.
Each of the volcanoes in the Auckland volcanic field has originated from a deep source of magma and everytime there has been an eruption, it has been of a new batch of basaltic magma. A crucial aspect of this particular style of volcanism is that there is no crustal magma reservoir present between the eruptions so there is no source of heat to drive the geothermal systems as there is in the central North Island. Page 3 of 19 This lack of surface activity in the Auckland field leads to the mistaken fact and confirmation that the field is extinct whereas nothing could be certainly concluded.
The only other active basaltic volcano zones in New Zealand are found in the Northland region near Whangarei, around Kaikohe and in the Bay of Islands. It seems to be that these are the areas where the crust is stretching gradually which causes the magma to rise through the cracks. Millions of years ago, similar activity lead to the formation of the volcanoes in the Banks of Peninsular and Dunedin regoin, but eventually causing them to be extinct. Eruption History One of the most serious obstacles there is in working out the volcanic history of the Auckland field is that the volcanic rocks themselves are very difficult to date.
Most of the available ages of eruptions come from wood or shell material, which has been buried during an eruption. This material can be analysed for its radioactive carbon content and this information can be used to calculate an age for the eruption. The problem is that the carbon method of dating is only useful back to about 40,000 years before the present. Recently, other methods of dating have been indicating that the oldest eruptions in the Auckland field may have occurred as much as 150,000 years ago. page 4 0f 19 Source: http://gns. cri. z Timeline of the AVF Of the 49 eruptions in the Auckland volcanic field, 19 of them are known to have occurred within the last 20,000 years. Of these 19 volcanoes, about 18 of them erupted between 20,000 and 10,000 years ago. By comparison, there were only 21 eruptions between 20,000 and 100,000 years ago, and about 9 eruptions earlier than 100,000 years ago. The area covered by each volcanic centre is generally localised within a kilometre or so and the total volume of erupted material is small.
The Essay on Thirty Years From Now
As I sit here, I wonder what I will become; all I see is pure success like no one has ever seen. My life is full of great and achievable goals that can fulfil my life with happiness. I see myself see myself thirty years from now becoming the most successful person the world has seen. I will have graduated high school and college with 4.0 GPA, majoring in aeronautical engineering while being in the ...
Nonetheless, five of the volcanoes such as Mt Mangere, One Tree Hill, Three Kings, Mt Eden and Mt Wellington are of medium size volcanoes. Page 5 0f 19 The largest, Rangitoto, is an exceptionally large volcano for the field, contributing 59% of the total volume of erupted material. It is a significant fact, that the five medium-sized eruptions occurred between 20,000 to 10,000 years ago and that the largest eruption such as Rangitoto was only about 600 years ago. Source: http://gns. cri. nz Mt Mangere,Auckland
Also the amount of volcanic deposits produced in the eruptions over the last 20,000 years are far greater than the preceding volcanoes about 20,000 years ago. There emerges to be a trend towards the increase in the average size of eruptions but it is uncertain to be sure whether the next eruption will be a small, medium or a large sized activity. Page 6 0f 19 Case Study : Rangitoto Island Rangitoto Island is a volcanic island in the Hauraki Gulf just off the coast of Misson Bay in Auckland, New Zealand.
It is an symbolic landmark of Auckland as its unique symmetrical 850 feet high shield volcano cone is visible from around of the city. It is the most recent and the largest of the approximately 49 volcanoes in the Auckland Volcanic Field. Source: http://upload. wikimedia. org A view of Rangitoto from North Head Rangitoto stands for ‘Bloody Sky’ in Maori with the name derived from the phrase “Nga Rangi-i-totongia-a Tama-te-kapua” meaning ‘the days of the bleeding of Tama-te-kapua’.
The Term Paper on Absolute Dating Carbon Potassium Archaeologists
Ideally, analysis of the materials found on a site begins in the field laboratories while excavation is still in progress. Often, however, reconnaissance and excavation are completed in a relatively brief period of time, and the records and preserved remains are taken back to a museum, university, or laboratory for more analysis. This analysis has many aspects, which include describing and ...
Tama-te-kapua was the captain of the Arawa waka and was badly wounded on the island during a battle, that was fought and lost at the Islington Bay. Page 7 0f 19 History of Rangitoto Rangitoto was formed by a series of eruptions between 600-700 years ago. Scientists have disputed about the length of the eruptions, which are thought to have lasted with interruptions for about 10 to 200 years. In any case, the amount of material that erupted from the volcano was equal to about the combined material of all other eruptions in the Auckland Volcanic Field before.
Source: www. scoop. co. nz The first segment erupted most of the volcanic ash that surrounds the Motutapu Island next door, and then produced the lower, northern, scoria cone. The second segment built most of the Rangitoto island erupting all the lava flows and forming the main scoria cone at the apex. The 2. 3 cubic kilometres of material that erupted from the volcano was about equal to the combined material produced by all the previous eruptions in the Auckland volcanic field, which were spread across for over 250,000 years. Page 8 of 19
However, the volcano is not expected to become active again as some of the facts gathered have shown a likelyhood of future eruptions. Reducing the matter during the cooling process has left a wide ring around the crater summit which can be viewed from the highest point. The island is considered especially significant because of all the stages from raw lava sediments and fields as to the scrub establishments and sparse forests that are visible. In some parts of the island, fields of lightweight,black lava stones are still exposed in the area, appearing very new to the casual eye.
Visitors that walk through the lava fields have also walked through some of about the seven known lava caves present within the island. Source: en. wikipedia. org Lava tubes form when low-viscosity molten lava known as pahoehoe flows through and cools on the outside due to the contact with the low ground and air to form a hard crust, allowing the still-liquid molten lava to continue to flow through the inside. At Rangitoto, there are large tubes present that are cave-like and in some cases, a torch is required to explore the caves.
The Essay on The Process of Carbon Dating
27 February 1940, by Martin Kamen and Sam Ruben at the University of California, although its existence had been suggested by Franz Kurie in 1934. - This is used in chemical and biological research, in a technique called carbon labelling. Carbon-14 atoms can be used to replace nonradioactive carbon, in order to trace chemical and biochemical reactions. - It is produced in the upper layers of the ...
By comparison, the longest known cave is about 50 m long. Page 9 of 19 Flora and Fauna Although, different species of plants seem to exist there is no such form of streams on the island. Therefore, the plants heavily rely on rainfall for moisture. Rangitoto has the largest forest of pohutukawa trees in the world. In overall, more than 200 species of trees and flowers survive on the island, including several species of orchid, as well as more than 40 types of fern.
Source: fickle-goingoutdoors. blogspot. com Summit of Rangitoto Island Page 10 of 19 As lava fields contain no soil of a particular kind, wind carried matter and slow breaking-down processes of the island’s flora are still in the process of transforming the land into a more habitable environment for most plants, which is one of the reasons why the local forests are compararitively young and do not yet support a large bird population.
Goats existed on Rangitoto in large numbers in the mid 19th century, but were eventually eradicated in the 1880’s. The Fallow deer species were introduced to the Motutapu island in 1862 and had spread to Rangitoto over time, but due to tough conditons they disappeared by the 1980s. By 1912, the brush tailed rock wallaby was common in Rangitoto, as the brushtail possum was later introduced in 1931 and again in 1946. Both were eradicated in a campaign from 1990 to 1996 using cyanide poison and dogs.
Over time, Stoats, rabbits, mice, rats, cats and hedgehogs remained a problem on the island, but the Department of Conservation aimed to eradicate all species that were a threat to the island, beginning with the poisoning of black rats, brown rats and mice. In August 2011, both Rangitoto and the neighbouring Motutapu Islands were officially declared pest-free with both islands now also increasing in populations of newly translocated saddlebacks. Page 11 0f 19 Radiometric Dating * Potassium-argon dating method (K-ar) * Carbon-14 Dating Method (14C)
Potassium-argon Dating Method The k-ar method determines the time of the origin of rocks by measuring the ratio of radioactive argon to radioactive potassium in the rock. This dating method is based upon the decay of radioactive potassium-40 to radioactive argon-40 in minerals and rocks. Thus, the ratio of argon-40 and potassium-40 in a mineral or rock is a measure of the age of the sample. On the other hand, the abundance of argon in the Earth is relatively small because of its escape to the atmosphere during processes associated with volcanism.
The Term Paper on Carbon Dating Sample Samples Radiocarbon
Introduction The discipline of archaeology can open up the past to us in a way in which we can enter into a dialogue with our ancestors. There are many ways it can do this: stratigraphic excavation, pottery typology, socio-historic interpretation, etc. However, one thread running through this increasingly focused pursuit is that of dating the physical findings to a particular cultural timeline. ...
The potassium-argon dating method has been used to measure a wide variety of ages. This particular method of dating has a very long half life of 1. 3 billion years, by doing so scientists are able to calculate the age of when a certain organism had died. In some cases, the potassium-argon age of some meteorites have been dated as old as 4,500,000,000 years, and volcanic rocks as young as 20,000 years old have been measured by this method. Page 12 of 19 Advantages of Potassium-argon Dating Method
Potassium-Argon dating has the advantage that the argon element is an inert gas that does not react chemically and so therefore would not be expected to be included in the solidification of a rock, so any argon found inside a rock is very likely the result of a radioactive decay of potassium. Since the argon escapes if the rock is melted, the dates acquired are specifically to the last molten time for the rock. One thing to note about K/Ar dating method is that it will never provide an overestimate of the age,hence, making it a good tool for determining lower bounds of materials
Disadvantages of Potassium-argon Dating Method The only disadvantage for this particular method is that due to the element’s long half-life, the technique is most applicable for dating minerals and rocks more than 100,000 years old. For shorter timeframes, it is very likely that not enough Argon 40 will have had the time to accumulate in order to be accurately measured and dated. Page 13 of 19 Carbon-14 Dating Method All organic materials have decaying Carbon-14 present in them.
However, plants and animals that are still alive consistently replace the supply of carbon in their living systems and so the amount of Carbon-14 present in them stays almost constant. Once a plant or an animal dies, the Carbon is no longer being replenished and so the Carbon-14 element starts to decay. In this particular way, by measuring the amount of Carbon-14 in the body of a prehistoric animal or plant, scientists can state when the plant or animal had died. All radioactive materials have a half-life. In this case, the half life of the carbon-14 element is stated about 5,568 years.
The Essay on Is Carbon Dating Accurate
Is carbon dating accurate? Carbon dating, used since 1948, is currently the main method of testing artifacts for age. My objective through this essay is to disprove the accuracy of the Carbon 14 dating method. William Libby invented carbon dating in 1948. It works on the principle that the carbon 14-C, is radioactive. It decays at a? known? rate called a half-life. This is balanced by the fact ...
If an organism has a certain amount of a radioactive material, its half-life is the time it takes for half of the material you started out with to decay. Advantages of Carbon-14 Dating Method Carbon-14 dating as an advantage to the field of chemistry is that it is a way of determining the age of a certain archeological artifact of a particular origin up to about 50,000 years old. It is used in dating things such as bone, cloth, wood and plant fibers that were created in the recent past by human or natural activities.
Page 14 of 19 Disadvantages of Carbon-14 Dating Method The carbon-14 dating method becomes less accurate over about 50,000 years and it should not be used to date artifacts over about 100,000 years old. When a particular organism dies, it stops absorbing carbon-14 as the carbon-14 already present in its body starts to transform into carbon-12. The ratio of the carbon-14 to carbon-12 in the remains of a biological organism indicates how long it has been dead.
This method assumes that the carbon-14 / carbon-12 ratio in the atmosphere over the last 50,000 or so years have remained the same as it is today, which can be a potential source of error when measuring an artifact. Another problem that arises wit this dating method is that, if a person picks up the mineral or the organism with his bare hands, some of the carbon from his skin may have mixed with the sample, causing it be contaminated and not eligible to carbon date it. Conclusion
After researching various radiometric dating methods, I have come to conclusion that neither of the methods can be considered completely accurate as they cannot fully determine the age of a certain object. Page 15 of 19 There is always an assumption that is made which is, the amount of carbon-14 in the atmosphere has always remained the same. Whereas, the amount of carbon-14 in the atmosphere has actually been increasing. It has not yet come to a stop but has been estimated that it would take roughly 30,000 years for the earth to reach its equilibrium.
One of the problems was that, scientists believed that the earth was billions of years old as they had assumed that the carbon-14 element had reached its equilibrium under false assumptions. The fact is that it hasn’t, there is more carbon-14 present in the atmosphere today than there was a decade ago. Meanwhile, on the other hand, the K-ar dating method also seems to be an inaccurate call of stating the age of a particular rock or a mineral. The Potassium-Argon dating method can preferrably date older rocks and fossils than using carbon-14 because it has a longer half-life of 1. billion years. The potassium in an organism or object decays to argon and the half-life is determined by measuring the number of particles that decayed in a 3 to 4 day period, then concluding the time it would take for half the sample to decay. Scientists believe that the lava, also known as basalt, has no argon in it when it erupts from a volcano. It states that after the lava erupting, the potassium starts to decay to argon, now because it starts without argon, the basalt is assumed to be the perfect substance to date. Page 16 of 19
To me, this doesn’t seem to be a very accurate way to measure the half-life, specially considering the half life to be a billion years. After researching to prove my statement with evidence, I have come across certain facts that would prove the inaccuracy of the potassium-argon dating method. Here are some of the examples I have found regarding the dating of volcanic lava : * Basalt from Mt. Etna, Sicily from an eruption in 122 BC gave an age of 250,000 years old, when we know it is less than 20,000 years old * Lava from the 1801 Hawaiian volcano eruption gave a date of 1. million years old when it was only 200 years old. * Basalt from Mt. Etna, Sicily gave an estimated age of 350,000 years old when it had only erupted in 1972. This shows that radiometric dating methods can’t be fully depended on, due to the lack of consistency and the large margin of error it is capable of.
