Brief Explanations of Various Geologic Phenomena Around the World

1. The Bay of Fundy has famously high tides because of tidal resonance, a rocking motion of the water called seiche, and the shape of the bay itself. Tidal resonance is the natural tides (rise and fall the water level) in the bay caused by the gravitational pull of the sun and moon. The tides are compounded by a phenomenon called seiche, which is the movement of water caused by wind—like the back and forth sloshing you can observe when you splash in your bathtub. The water movement caused by the seiche exaggerates the tides because the time it takes for the water to slosh from one side of the bay to the other is just about the same amount of time between the tides. The seiche’s movement is easily maintained and reinforced by the tide, like the movement caused by an adult pushing a child on a swing: “just a very small push is required to keep the swing moving” (Fundy Guild Inc. at Fundy National Park). The tides are already exaggerated because of these phenomena, but high tide is even higher due to the shape of the bay: it’s narrower and shallower in its upper portions, which forces the already large quantities of water to climb higher on the shore (Fundy Guild Inc. at Fundy National Park).

2. A temperature inversion is when the atmospheric temperature increases with elevation. It could potentially increase the level of atmospheric pollution because the overlying layer of warm air could trap smog in the lower layer of air closer to the city, rather than permitting smog to dissipate in the higher layers of the atmosphere as it usually does. The Great Smog of 1952 lasted for 4 days, killed thousands, and “remains the deadliest environmental episode in recorded history” (Nielsen, 2002). In that period, burning coal for household use was still very common in London. Normally the smoke and pollution from coal fires would dissipate in higher atmospheric levels rather than remain at a city level, but in December of 1952, a bout of cold weather caused Londoners to burn more coal than usual. This increase in coal pollution was exacerbated by windless conditions and a temperature inversion that settled over the city, which created a “lid” over London and trapped all the coal smoke. The event shut down the entire city—cars couldn’t be driven and even walking was out of the question because people couldn’t see their feet. Food markets, businesses, and performances were all shut down because, according to one Londoner, “it was like you were blind” (Nielsen, 2002). While such unprecedented pollution levels were tragic, there is a silver lining to the smog: after the disaster people became much more aware of the effects of pollution and more clean air legislation was passed, such as the Clean Air Act 1956 (BBC, 1956).

3. Seasonal variation of air pollution can be difficult to quantify because different kinds of particles appear at different times, due to factors such as the fuels used in different geographic regions and the seasonal variation of human activity (such as wood burning in the winter and air conditioner use in the summer). Despite the number of confounding variables, the consensus seems to be that air pollution in large cities seems to be at its worst in the summer in the late afternoon. A study done by researchers at Johns Hopkins measured pollution levels of different geographic regions in the United States and found that although mortality levels generally increase in the fall and winter, “the (particle) estimate for summer is more than twice as large” than other seasons across different regions (Peng, Dominici, Pastor-Barriuso, Zeger, & Samet, 2004). Certain pollutants react with sunlight and form different, more harmful compounds, so in the summer when there are longer days and generally more sunlight in the Northern Hemisphere, more reactions occur. In the summer there is “more stability in the atmosphere” so the air doesn’t move as much, meaning the existing pollutants and those created by photochemical reactions stagnate right above the city (Mascarelli, 2011).

4. As elevation increases, air pressure decreases. The atmosphere is made up of gases which have atomic mass. As elevation increases, there is less atmosphere above the location in question, and less atmosphere means less mass and therefore less pressure.

References

BBC News. (1956). 1956: Thick Fog Causes Death on Roads. BBC. Retrieved from http://news.bbc.co.uk/onthisday/hi/dates/stories/december/19/newsid_3280000/3280473.stm

Fundy Guild Inc. at Fundy National Park. Tides of Fundy.

Nielsen, John. (2002). The Killer Fog of ’52: Thousands Died as Poisonous Air Smothered London. NPR. Retrieved from http://www.npr.org/templates/story/story.php?storyId=873954

Peng, R.D., Dominici, F., Pastor-Barriuso, R., Zeger, S.L., & Samet, J.M. (2004). Seasonal Analyses of Air Pollution and Mortality in 100 U.S. Cities. American Journal of Epidemiology. Retrieved from http://aje.oxfordjournals.org/content/161/6/585.long