A nearby volcano, Lava Mountain, threatens Hazard City. The major volcanic hazar

Question

A nearby volcano, Lava Mountain, threatens Hazard City. The major volcanic hazards to be aware of are: tephra, lava flows, pyroclastic flows, lahars, and volcanic gases.

Tephra is the term used for volcanic rock that is explosively ejected out of a volcano.

Lava flows occur when hot liquid lava erupts from a volcanic vent.

Pyroclastic flows are hot mixtures of gas and rock fragments that erupt explosively from volcanic vents.

Lahars are mixtures of water and rock fragments that flow downhill and in river valleys.

Volcanic gases are continuously released from volcanic vents and can be very dangerous.

Those that pose the greatest risk to humans and their property are carbon dioxide, sulfur dioxide, and hydrogen fluoride.

Use the following links:

The links below contain data for this activity. http://media.pearsoncmg.com/ph/esm/esm_hazardcity_4_standalone/assignment02/county_map.htm http://media.pearsoncmg.com/ph/esm/esm_hazardcity_4_standalone/assignment02/city_map.htm http://media.pearsoncmg.com/ph/esm/esm_hazardcity_4_standalone/assignment02/local_climate.htm http://media.pearsoncmg.com/ph/esm/esm_hazardcity_4/volcanic/pcflows.html (and the sub-links within it too)

Part A answer is here: http://www2.gsu.edu/~geohab/Babaie/pages/geol2001/Hazard_City/4_volcanic_hazard_assignment_solution.htm

Part B - Lahar Risk

Why is Hazard City at more risk for lahars than Hutton or Wrightstown, even though they are closer to Lava Mountain than Hazard City?

(C) Lahars follow stream channels

(D) All the glaciers on Lava Mountain are on the eastern side.

Part C - Evidence of Lahars

Utilizing the county map, which of the nine locations where subsurface materials have been determined show evidence of lahars?

Utilizing the county map, which of the nine locations where subsurface materials have been determined show evidence of lahars?

Part D - Thickest Ash Deposits

Which city would you expect to have the thickest ash deposits from previous eruptions?

Part F - The Future Lahar Risk

There is no evidence of past lahars for many of the neighborhoods in Hazard City, but they could still be affected in future eruptions. Which of the following communities is least likely to be affected by lahars in future eruptions?

Part G - The Composition of Lava Mountain

Based on the evidence of past lava flows, what is the composition of Lava Mountain?

Part H - The Volcano Mountain Type

Based on the features of Lava Mountain, what type of volcano is it?

Part I - Lava Flow Speeds

Based on the composition of the lava, approximately how long would it take for the lava to have flowed from the vent of Lava Mountain to the base?

Part J - The Eruption of Volcanic Gases

Which of the following eruptions belched out the highest total percentage of dangerous volcanic gases?

Momotombo

Part K - The Pyroclastic Flow Risk

If Lava Mountain erupts, which of the following communities is at the greatest risk from the basal flow of a pyroclastic flow?

(A) Lahars are affected by wind patterns. (B) Lahars do not begin to form until several miles away from a volcano.

(C) Lahars follow stream channels

(D) All the glaciers on Lava Mountain are on the eastern side.

Part C - Evidence of Lahars

Utilizing the county map, which of the nine locations where subsurface materials have been determined show evidence of lahars?

Utilizing the county map, which of the nine locations where subsurface materials have been determined show evidence of lahars?

(A) 4, 5, 6, 7 (B) 5, 2, 8, 4 (C) 4, 3, 6, 9 (D) 2, 4, 6, 9

Part D - Thickest Ash Deposits

Which city would you expect to have the thickest ash deposits from previous eruptions?

(A) Hutton (B) Blaney (C) Crossroads (D) Hopper

Part F - The Future Lahar Risk

There is no evidence of past lahars for many of the neighborhoods in Hazard City, but they could still be affected in future eruptions. Which of the following communities is least likely to be affected by lahars in future eruptions?

(A) Ralston (B) Walnut Heights (C) Riverside (D) Hickory Estates

Part G - The Composition of Lava Mountain

Based on the evidence of past lava flows, what is the composition of Lava Mountain?

(A) dacite (B) andesite (C) basalt (D) granite

Part H - The Volcano Mountain Type

Based on the features of Lava Mountain, what type of volcano is it?

stratovolcano cinder cone shield lava dome

Part I - Lava Flow Speeds

Based on the composition of the lava, approximately how long would it take for the lava to have flowed from the vent of Lava Mountain to the base?

less than 5 minutes 8–9 hours 3–4 days 1–2 hours

Part J - The Eruption of Volcanic Gases

Which of the following eruptions belched out the highest total percentage of dangerous volcanic gases?

They were all equally dangerous. Erta Ale Kilauea

Momotombo

Part K - The Pyroclastic Flow Risk

If Lava Mountain erupts, which of the following communities is at the greatest risk from the basal flow of a pyroclastic flow?

Wrightstown Hopper Hazard City Hutton

Explanation / Answer

Answer Part B: Lahar follow stream channel.

Hazard city is at more risk due to Lahar as compared to Hutton or wrightstown due to the fact that Lahars follow stream channel as mentioned in "Lahars are mixtures of water and rock fragments that flow downhill and in river valleys"

Part C: Answer B (4,5,6, 7)

These are the locations where mud and stream sediments have been found in drilling.

Part D: Answer A, Hutton has the thickest Ash Deposit

Explanation: Rest of the cities i.e. Blaney, Hooper and Crossroads are located in the upwind direction that is the reason the drill holes around these locations does not show ash content.

Part F: Answer B, Walnut Height

The Hickory estate and Walnut height both can be considered as less prone to future Lahar risk as Lahars follow stream channel. This is further supported by drill holes between river and Hickory estate which does not intersect Mudflow deposit.

Thus it can be concluded that walnut height being the farther than Hickory estate is least prone to Lahars in future.

Part G: Answer B: Andesite

This has been ascertained based on the lava mountain structure and presence of different constituent. Andesite being less viscous than Basalt is ususally associated with lava domes.

Part H: Answer A,

The Mountain volcano type is seems to be Stratovolcano

Part I: Answer D

SInce Andesitic Lava has a flow speed of few Km/hour, it can be concluded that the lava will take few hours i.e. 1-2 hoours to reach the base which is approximately 4-5 Km.

Part K: Answer D

Hutton being the closest and on the downslope is of greater risk.

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