Sample Geology Coursework Paper on Volcanoes


QUESTION: The map in Fig. 1 shows the major volcanic centers in the Cascade Range and surrounding population centers. Which volcano(es) pose(s) the greatest geologic hazard to the following population centers listed in Table 1 below?   

Table 1

Population CenterVolcanoes
Seattle/Tacoma, WA Glacier peak and Mt. Rainer
Bellingham, WAMt. Baker
Mt. Vernon, WAMount St. Helens
EugeneBelknap Shield volcano, Mt. Bachelor, Creator lake, Mt. Washington, Mt. Jefferson, South sister, Three Sisters Broken top
PortlandMt. Hood and Mt. St. Helens

QUESTION: Which do you think has the potential to be more destructive: A convergent margin volcano like Mt. St. Helens that erupts about once every century, or one that erupts at much longer intervals? Why do you think this is so? 

A convergent margin volcano is less destructive as compared to that that erupts at a much longer interval. This is because the even though convergent margin volcanoes have a lesser reoccurrence period, only a smaller percentage of the eruption cause fatalities and hazard to crops due to the ashes produced. On the other hand, the volcanoes that erupt after much longer intervals are result to very large eruptions that cause serious fatalities thus being more hazardous even though they are mostly dormant.

QUESTION: Study Figure 3 (Cascade Eruptions During the Last 4000 Years) and 4 (Annual Probability of Tephra Accumulation). Where is the main area of concentration of tephra accumulation? 

The main area of concentration of Tephra accumulation is at Mount Saint Helens in Washington.

QUESTION: What are the main factors that control the spatial pattern of the annual probability of 10 cm or more of tephra accumulation in the Pacific Northwest from Cascade volcanoes?  

This includes; the rate of release of gasses dissolved on the magma, the size of the tephra particles released as small particles and the column height of the released particles rise more than 10 km upwards and covers longer distances downwards. Besides this, the eruption volume from the ash cloud may lead to thicker layers or thinner layers of particles formed on land.  Wind speed and direction of flow also control the spatial pattern.

QUESTION: On the day of the main Mt. St. Helens eruption, seismometers 3.5 miles from the blast origin stopped transmitting 77 seconds after the eruption, when they were overridden by a dense pyroclastic blast cloud. Based on this information, how fast (in miles per hour) was the blast cloud moving? Show your math.   

60 seconds =  1 min

77 seconds = ??                       77/60

Therefore, if Mt St Helens erupts 3.5 miles for 77/60 min, what will it be in 60 min

77/60 = 3.5

60    =??      (60 X 3.5) / (77/60) = 163.64miles per hour

QUESTION: What population centers are built on top of the Osceola Mudflow? You will need to zoom in on the map to read the names of the towns.

Orting, Sumner, Auburn, Puyallup, Buckley and Enumclaw centers


CommunityDistance from base of the volcano (km)Distance from base of the volcano (m)Response Time (seconds)Response Time (minutes)
Kent    16.816800181080
Tukwila     10.110100241440

 QUESTION: What physical and ecological changes have affected many of the river valleys (lahar flow paths) since the arrival of European settlers in the 19th and 20th centuries?    

Industrialization and increase in number of vehicles have been known to increase the rate of greenhouse gases in the atmosphere. Besides this there has been an increase in the rate of burning of fossil fuels together with deforestation which largely contribute to global warming. The high temperature from global warming results to melting of glaciers and ice snows which forms water that mixes with lahar eventually resulting to lahar flow paths.

QUESTION: What impact might such changes have on the potential distance and flow velocity of a recurrent flow? 

The above changes results to reduced velocity of the lahar flow thus increasing the speed at which the lahar flows. Therefore, the lahar flow path is able to flow to longer distances due to its reduced velocity.

QUESTION: Assuming an average recurrence interval of 10,000 years for an Osceola-sized lahar event, how would you advise city planners in Enumclaw, WA, regarding site location within city limits for:   

A. An elementary school      

The school should not be located in a valley landscape area. It should also be set far away from any volcanic mountain and the school should be equipped with warning system which would help in alerting everyone in the school in case of lahar threats. The elementary school should thus be built on a higher ground. This is because the lahar flows downwards according to the area’s gradient and topography.

 B. A nuclear power plant 

The nuclear power plant may result to grave damages in case it is destroyed by the lahar event. It is thus not advisable to construct the nuclear power plant in the area since there will be likelihood of a lahar event.

QUESTION: Study Figures 5 (Glacier Peak Eruption History) and 6 (Areas Inundated by Glacier Peak Debris Flows).  What relationship do you see between the recurrence interval of volcanic eruptions and the size of the debris flow?     

The longer the recurrence interval of volcanic eruptions the larger the size of the debris flow and the shorter the recurrence interval the smaller the size of the debris flow.

QUESTION: You will notice that a large debris flow inundated the Stillaguamish River valley between 12,500 and 13,100 years ago. What factor(s) might account for the subsequent large debris flow event to inundate the Sauk and Skagit River valleys 6300-5900 years ago and no longer flow into the Stillaguamish River valley? 

The factors that are likely to be accountable include the large size of River Sauk and Skagit, The channel gradient of the rivers such that Sauk might have a steeper gradient as compared to Stillaguamish river valley and the rate of erosion of Sauk’s river bed thus increasing the size and space for deposition of the large debris.

QUESTION: Study the USGS map HA-729 Sheet 2, “Modern Debris Avalanches and Debris Flows at Mt. Rainier, Washington.” (ON CANVAS) What are the three most common factors causing debris avalanches on Mt. Rainier?   

  1. Volcanic eruptions causing instability of the slope
  2. Vibrations caused by earthquake
  3. Undercutting of cliffs and banks by waves or river erosion
  4. Intense or prolonged rainfall, rapid snowmelt, or sharp fluctuations in ground-water levels

QUESTION: Based on information provided to you from the above volcanic hazard map, do you think that debris avalanches pose a threat to any of the URBAN areas of the Puget Sound region? Why or why not?

Yes. This is because of the fact that Puget Sound region is found a lowland area which has a steeper gradient. Besides this, the rate of melting glacier is rapid thereby posing danger to Puget Sound area. A landslide is likely to occur in such areas and may result to great fatalities such as destruction of houses and properties and worse; death.

QUESTION: An outburst flood from which glacier system would pose the greatest risk to the town of Longmire?

Mt. Rainier river system

QUESTION: A velocity of about 50 meters per second, which was increasing at the point of measurement, was reported for the 1980 debris avalanche at Mt. St. Helens. If these data can be extrapolated to a potential Mt. Rainier debris avalanche, how long would the citizens of Longmire have to react to a debris avalanche generated at the terminus of the Nisqually Glacier?     

10 seconds