2. You are reassigned as regional manager for Denyallclaims Insurance Company in
ID: 284367 • Letter: 2
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2. You are reassigned as regional manager for Denyallclaims Insurance Company in the El Centro area, and the executives at the main office assign you a new task. A company is requesting insurance coverage on a ski resort they are planning to build in a South American country bordering on the Pacific Ocean. The ski resort will be built at the base of a conical mountain peak where a valley cut into the side of the mountain empties onto a broad flat plain. You are asked to evaluate the risk of building in this locality. Since you suspect that the mountain is a stratovolcano, you decide to go check it out for yourself.
Upon arrival at the site, you find that there are few rocks or deposits exposed on the valley floor that might give you a hint as to what has been happening at this mountain in the recent past. There are rumors among the people living nearby that the mountain has erupted a couple of times in the past few hundred years, but this is nothing to worry about, as it has been a long time since the volcano erupted and the locals consider it to be an extinct volcano. Because you have taken a course on natural disasters, you realize that relying on local rumors may cost you your job, your home now in Felicity (the center of the World), and maybe even your spouse, you decide to acquire more information.
You find a local geological consulting firm that is capable of drilling a hole 75 meters deep into the valley floor. The company will take core samples of the entire drill hole, and, if they encounter any charcoal within the samples, provide you with 14C age dates of any charcoal they find. When finished, they provide you with a chart (shown below) that shows the depth within the drill hole, a description of the deposits found in the drill hole, and the 14C age of the charcoal they found in the layers (shown as numbers within the layers). Because a 14C age date on charcoal is the date when the original tree or twig died due to exposure to hot volcanic material, it gives a fairly precise date on the eruption which caused the formation of the charcoal. The drill hole data gives a fairly complete picture of the events that have occurred at this particular locality. Other eruptions may have occurred, but they did not leave deposits in this valley.
From your text and class discussions (and further investigations on your own) you know that pyroclastic flow deposits result from Plinian and Pelean eruptions (very explosive), and scoria fall deposits and lava flows result from Strombolian eruptions (less explosive). Mud flows can form during an eruption or during periods of heavy rains not associated with eruptions. Viscosity and gas content of magmas are the two properties most responsible for explosive volcanic eruptions and both of these properties generally increase with increasing SiO2 content of the magma.
From this information, you want to answer the following questions for your report to corporate headquarters.
a. Describe in general how the history of the volcano, as determined in this particular valley, has changed through time as revealed by the deposits found with depth in the drill hole. In particular note how the SiO2 content of the magmas has changed with time and whether or not this is reflected in the explosivity of the eruptions as revealed by the deposits.
b. Note that the drill hole data shows two distinct periods of eruptive style of the volcano as exhibited by the deposits. How would you characterize these different periods and when did the change occur?
c. The average eruption rate, R, (number of eruptions/year) can be obtained by dividing the number of eruptions by the time over which the eruptions occurred*. The average eruption frequency (number of years between eruptions) is then 1/R. What is the average eruption rate and average eruption frequency for (i) the entire sequence represented by the layers represented in the drill hole and (ii) the two different eruptive periods? (Note that in counting eruptions, it is likely that two deposits of different type that have the same 14C age date, probably represent a single eruption)
*Note that in considering the time periods for this exercise, you should use the range from the first eruption of the period to the beginning of the next period. For example the time range for the entire sequence should be 1300 minus 0, the time range for the first eruptive period should be1300 minus the date of the beginning of the next period, and time range for the second eruptive period should be the date of the beginning of the second eruptive period minus 0).
d. What are the three most likely volcanic hazards expected in this valley?
e. Based on the above information what can you tell the Denyallclaims corporate headquarters about the risk of building a ski resort at this locality?
0-SSSS1201 Mud Flow Deposit 120 Rhyolitic Pyroclastic Flow Deposit Rhyolitic Pumice Fall Deposit 120 15 190 Rhyolitic Pumice Fall Deposit 20 190 Rhyolitic Pyroclastic Flow Deposit 230 Mud Flow Deposit 25 230 Rhyolitic Pumice Fall Deposit Rhyolitic Pyroclastic Flow Deposit 30 290 Andesitic Pumice Fall 330 E 35 Andesitic Pumice Fall E 40 360 400 Andesitic Pyroclastic Flow Deposit 45 400 Andesitic Pumice Fall Deposit R&SR6301; Mud Flow Deposit 50 Andesitic Lava Flow 630 Andesitic Scoria Fall Deposit 55 890 Andesitic Lava Flow 60 890 Andesitic Scoria Fall Deposit 1020 Andesitic Lava Flow 65 1020 Andesitic Scoria Fall Deposit 1100 Basaltic Lava Flow 70 1100: Basaltic Scoira Fall Deposit 1300 Basaltic Lava Flow 75 14 age dates of charcoal found in depositsExplanation / Answer
answer- In the history of this flat valley region, there were occurence of 3 major volcanic eruption
1- first volcanic eruption occured between 1300 year to 630 year. characterize by basaltic lava flow, basaltic scoria fall deposit, andesitic scoria fall deposit, andesitic lava flow and mud flow deposit
2- second volcanic eruption occured between 400 to 230 year. charcterize by andesitic pumice fall deposit, andesitic pyroclastic deposit, andesitic pumice fall, Rhyolitic pyroclastic fall deposit, rhyolitic pumice fall deposit, and mud flow deposit. there presence rhyolitc fall deposit suggest that the volocano was more voilent or explosive condition.
3- third volcanic eruption occured between 190-120 year characterize by Rhyolitic pyroclastic flow deposit, Rhyolitic pumice fall deposit, Rhyolitic pyroclastic flow deposit and mud flow deposit.
from the study of drill core data it have been found that region is lying in volcanic eruption prone area and in the recent year there is occurence of voilent or explosive eruption which is characterize by Rhyolitic fall and rhyolitic pyroclastic deposit.
In the first volcanic eruption there were occurence of Basaltic flow which low in silica content from 1020 year and at the time second volcanic eruption there were occurence of andesitic volcanic eruption which is medium in silica concentration. from the 290 year and at the time of third volcanic eruption there were occurence rhyolitic magma which is higher in silica content. It have been suggest on increasing in time there were occurce of more silica content volcanic eruption.
basaltic and andesitic volcanic represent low explosive volcanic acitivity while the presence of rhyolic deposit suggest the very explosive volcanic activity which tooks place after 290 year till now
answer- there is presence two eruption style
1- non explosive to low explosive volcanic eruption- from 1300 year to 330 year. In which from 1300 to 1100 year characterize by basaltic deposit which is non explosive in nature and from the 1020 to 330 year is characterize by the andesitic deposit which represent low explosive volcanic eruption
2- very explosive volcanic eruption- from the year to 290 year there region is characterize by the occurence by the Rhyolitic deposit which represents the very explosive volcanic eruption
answer- the threee most volcanic hazards occurs in this reigon are following
- pyroclastic flow of rhyolitic deposit which are highly explosive and less viscous in nature and they have ability to flow at very rapid speed
- fall deposit of explosive volcanic activity
- mud volcanism- volcanic acitivity+ mud+ water. it carries huge amount of debris along withit
answer- yes i will inform to Denyallclaims corporate headquater about the risk of this locality. It will suggest them not make any kind of resort in this region because it lies in highly volcanic activity prone area. there is occurence of highly explosive volcanism which could be harmfull for human lifes.
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