Download Kelsey Beechler ERTH 201 Lab East African Rift Valley Rift valleys

Kelsey Beechler
ERTH 201 Lab
East African Rift Valley
Rift valleys are valleys created by tectonic movement. They have steep sides, flat
floors, and are formed where the Earth’s crust is spreading. This type of spreading
tectonic movement leads to new land formation, as seen in the ocean with the MidAtlantic ridge where new oceanic crust forms at the sight of spreading. The region we are
looking at is the African Plate, which hosts the East African Valley. There are multiple
rifts intersecting and splitting off in this area. A theory behind the rifts is elevated
temperature in the mantle, causing bulging and stress on the plate, making the weaker
areas fracture (Wood). Major rifting systems concentrated in one area formed possibly
due to this. The major rifts in this area include the oldest Ethiopian rift, the Albertine rift,
and the Kenyan rift, which the last two make up the East African Rift (Wood). The region
today is undergoing a very unique activity. The African plate is splitting into two with all
these rifts. Most of the plate is separated onto a newly named section called the Nubian
plate, leaving the rest of the plate to the Somali plate (“Rift Valley”). Also within the East
African Rift Valley is a substantial amount of volcanic activity. Such volcanoes include
Mount Kilimanjaro and Mount Kenya. This is due to the tectonic activity, but it is
another geologic feature of the area that has a major impact on the surrounding
environment and land formation (NASA). This map shows the different plate boundaries,
developing plate boundaries, and their relationships to one another (Wood):
It is important to study the East African Rift Valley because it contains unique tectonic
activity. The causes of spreading and breaking apart of a continental plate are still
unknown. This is vital information scientists need to have in case this happens elsewhere
on the planet and what potential negative causes may occur due to this activity. Also, it
gives great insight into geologic movements, processes, and information about the type of
rock being affected. Lastly, it can give insight to if this occurred previously, in a
historical context, and what impact that may have had on the species inhabiting the
planet.
A triple junction is an area where three tectonic plates meet with three plate
margins. There are three types of margins involved with triple junctions and tectonics: a
ridge, a trench, or a transform fault (Alden). The way a triple junction is classified is by
the type of margins involved. This is done by giving each margin a letter, such as ridge
(R), trench (T), and transform fault (F) and then categorizing them to look like T-T-R or
something of those sorts. In the East African Rift Valley, the rifts have created a triple
junction. The point where the Nubian, Somalian, and Arabian plates meet in the Afar
region of Ethiopia on the African continent forms the triple-junction (Wood). Around this
triple junction, there is evidence of weaker, thinned crust, new-forming oceanic crust, and
stretching of crust, as seen in this picture:
This pattern of crust thinning is a product of the plates separating, allowing new crust to
form. The thinned crust is a mixture of volcanic and continental rock that once it gets to a
certain thinness oceanic crust breaks through (Wood). Since this is a triple junction, you
see this spreading and thinning in three different directions, with a large mass of thinned
crust in the center of all three. This expands the landmass of the area.
Continental rifting is a process that has many factors contributing to it.
Essentially, continental rifting is the breaking apart of a continental plate and the
accompanying divergent movements of those plates. The process begins by plate
divergence that possibly causes the continental plate to pull apart. This pulling action
weakens the plate, which already has some brittle characteristics, and causes some
earthquakes and breakage to occur. Once this occurs, hot magma starts pushing up and
causes pressure and bulging of the crust with magma convection. This pressure is
released through volcanoes. As more and more rock is melted due to the rising of the
magma level, the crust gets thinner. Eventually, when coupled with the spreading
movement, the plate breaks, allowing oceanic crust, or new crust material, to form
(Continental Rifting). The process of plates spreading is most commonly seen with
oceanic plates, such as with the Mid-Atlantic spreading ridge. On a continental plate it is
uncommon but is occurring in multiple places.
Climatic effects on an area can include anything from altitude changes,
presentation of new bodies of water, or geologic obstruction. The rising crust of the
eastern area of the rift valley has shown to block the moisture from entering Eastern
Africa from the Indian Ocean. This contributes to the climate becoming drier due to lack
of moisture. Aside from this, the mountain ranges are allowing certain wind currents with
moisture to enter certain areas of Southeast Asia. Lastly, the topographic changes have
been very noticeable. The land went from a flat, heavily forested region to a more
mountainous and dry region. When the earth was in the single continental mass called
Pangaea, the climate of the earth was very extreme. The oceans had massive storms and
the land had intense temperatures. The inland of the Pangaea continent was extremely dry
due to the lack of an oceanic coast or major body of water (Geology 150). The climate
today, with the continents broken up, is much more stable and diverse. There are smaller
chunks of land surrounded by oceans, lakes within the continents, and ice caps. Having
the land be at different latitudes also created variability in individual continent
temperatures.
Separation plays a huge role in evolution of all species. When presented with a
different environment, a species has to adapt and change. Over time, this leads to the
evolution of new and more diverse species. In rift areas, ridges are formed, land is
separating, and volcanoes form, all causing some geographical barriers. Also, due to the
changes within the geological features, ecological changes occur as well. With the
climate changes occurring, a humanoid species may have been accustomed to a forested
environment and the lifestyle associated with that, only to have the environment change
over time to a more mountainous region with a drier climate. These changes interrupted
natural, continuous gene flow, causing mutations and separate evolution of the different
populations (Kingston). As seen in this photograph, the evolution of the humanoid skull
changed drastically in different areas that were affected by this rifting process. They had
to change their habitat and lifestyle to accompany the new geologic features, so
eventually they physically changed as well, leading to diversity in the species.
The most interesting thing I learned about rifting would probably be the details of
the process itself. I know oceanic plates can separate and such, but I didn’t know that
continental ones could as well, and not just create new landmass, but also fully create
new plates. How such force could exist to pull apart and break continental crust is truly
amazing. It is also interesting to see how all these things correlate along the rifts, due to
the fact that so much occurs when plates spread. It really gives insight into how the world
is so interconnected through its different cycles and processes.