What are the three major types of plate boundaries found on earth and how are they different from each other?


Part A

What are the three major types of plate boundaries found on earth and how are they different from each other?

Convergent boundaries

Convergent plate boundaries occur when two plates come together and collide causing the thinner or more flexible plate to buckle beneath the more rigid plate, or in the case where both plates portray the same rigidity, results into crumpling and mountain ranges may be formed. Typically, when two oceanic crusts collide, island archs and/or trenches are formed; and in scenarios where an oceanic crust collides with a continental crust, the thinner oceanic plate is buckled below. A typical feature after the collision of tectonic plates is the formation of volcano chains and increased incidences of earthquakes along the convergent plate boundaries.

Divergent boundaries

Divergent boundaries form when two plates move away from one another, typically resulting into eruption of magma to form a crust. When such phenomena happens on dry land, rifts are usually formed while mid oceanic ridges are formed under sea. Important features that have been formed as a result of the formation of divergent boundaries include the Great Rift Valley and the Gulf of Aden.

Transform boundaries

Transform boundaries form when two tectonic plates slide over or past each other in opposite directions to meet at a lateral fault if on land or canyon if under sea. In the case of these boundaries, crust is neither created nor destroyed unlike in divergent and convergent boundary formation, but is simply cracked and broken along the lateral margins. Earthquakes are a common phenomenon as build up stress within the plates exceed the rock threshold resulting into the release of energy. The San Andreas Fault in California was formed as a result of two tectonic plates sliding past each other.

Part B 

For each type of plate boundary, give one example of a geographic location where that boundary exists.

Convergent plate boundary

Himalayan Mountains formed after collision of the Eurasian and Indian tectonic plates

Southern Alps formed after collision of the Australian and Pacific tectonic plates

Divergent plate boundary

The Great Rift Valley in East Africa

The Gulf of Aden separating the Horn of Africa and the Arabian Peninsula

Transform plate boundary

The San Andreas Fault in California

The Alpine Fault in New Zealand

q52: This essay question is about hurricanes.  Be sure to address all of the points below in your answer, and please write your answer in paragraph form.

What is a hurricane?

A hurricane is a massive rotating storm system that usually forms over the warm tropical and subtropical oceans and progresses towards the land. Other important features of hurricanes are;

They have a low-pressure center

Characterised by strong winds

Usually accompanied by thunderstorms and heavy rainfall

What gives hurricanes their power?

The key ingredient that powers hurricanes is water vapor. When ocean water evaporates, it absorbs heat energy from the warm ocean surfaces of tropical waters which is released as the latent heat of condensation when the water vapour condenses during the formation of clouds and thereafter rain. When there is little wind shear, this energy is not carried away but rather builds up resulting into formation of low pressure zones that consequently force wind currents to begin spiraling in the direction of low pressure area. The wind currents result into more water vapor being evaporated giving the hurricane even more power.

What aspect of a hurricane causes the most coastal damage?

The most coastal damage is formed as a result of storm surge which typically occurs when oncoming water currents driven by high winds from the hurricane rises rapidly. In most cases, these currents blow up roofs of houses built in low lying areas affected by hurricanes and in the worst case could as well as destroy these structures entirely if the winds are very strong. 

What is a storm surge?

A storm surge is a rise in the water levels e.g. of oceans caused by strong winds usually as a result of hurricanes. Storm surge are the main causes of destruction in low lying areas especially due to flooding and the effects of high pressure water currents on structures.

Why do hurricanes lose power when they hit land?

Since hurricanes derive their power from evaporating sufficient water vapor from warm water, crossing over land removes the hurricane’s energy source notwithstanding the cooler land temperature levels and increased surface friction with the ground terrain compared to the warm water surface, which ultimately decreases the hurricane’s winds and consecutively effectiveness.

q53: Explain at least four things that oceanographers can determine about past environmental conditions by studying marine sediments.  

The study of marine sediments especially those on quiet seafloors may be important in providing a details of recent events occurring in the water column above which they exist. Such information could provide useful insights in pollution, the natural marine habitat and changing oceanic water profiles over time.

Marine sediments are also important in determining past climates. The study of past climates is an important tool in modelling the current climate and environmental changes especially with regards to adaptation and mitigation measures.  

The study could also help unravel plate motions in different regions on the oceanic crust, and therefore explain the formation of oceanic features.

Evolution and extinction of fossils could also be traced from the study of marine sediments. In addition, the study of marine sediments has been used to determine the probability of occurrence of minerals and resources such as oil and gas. 

Marine sediments have also been used to determine the age of the sea floor and consequently the formation of important phenomena on both oceanic and continental crusts. These studies have contributed into robust theories and discussions into the formation of the earth.

Studying marine sediments could also assist oceanographers determine past coastal habitats for oceanic biological resources. This is important in development of present and future sustainability plans towards conserving marine habitats and environment in general especially with regards to preservation of endangered species.