Plate tectonics and rising sea levels

By Kayode Adeoye   |   04 November 2015   |   4:04 am  

sea-levelAs humans are breaking new grounds in technology and generally moving mankind forward with the benefits of such innovations, so also is the dynamics of the mechanics below the earth changing. Some experts are devoted to studying these changes to know their impact on the biosphere. One of such studies, the focus of this column for the week, was originally written by Julie Cohen from materials provided by the University of California, Santa Barbara.

The study itself was carried out by Associate Professor Alex Simms of the University’s department of Earth Science.
For millions of years, the Pacific and North American plates have been sliding past and crashing into one another. This ongoing conflict creates uplift, the geological phenomenon that formed mountains along the west coast of the United States of America. A new analysis by University College, Santa Barbara, UCSB earth scientist Alex Simms demonstrates that the Pacific coastlines of North America are not uplifting as rapidly as previously thought.

The results appear in the journal, Geological Society of America Bulletin. “Current models overestimate uplift rates by an average of 40%” said Simms, an associate professor in UCSB’s department of Earth Science. “They do not take into account glacio-isostatic adjustment, the earth’s response to the melting and growths of past ice sheets. Previous studies of the pacific coast, including California, have ignored this when trying to use past sea levels to calculate uplift rates.”

Uplift is the vertical elevation of the Earth’s surface in response to Plate Tectonics. Scientists determine uplift rates by measuring marine terraces; flat mesas that indicate where the ocean level used to be and comparing their elevations to geologic records of sea level change. However, traditionally used “global” sea level records come from places like the Huon Peninsula of Papua New Guinea, far away from the ice sheets that once covered Canada. That’s a problem because the freezing of water into ice sheets and its subsequent thawing actually changed the shape of the Earth ever so slightly and this deformation affects ocean levels. According to Simms, the land responds the way a mattress does, indenting from weight and then, relaxing back to its original shape. The Earth’s gravitation field also changes in response to the building up and melting of these ice sheets. These changes to the land and Earth’s gravity cause past sea levels to vary across the world. Most of the glacio-isostaticadjustment are not caused by current glacier melt but by one rebound of the Earth from the several-kilometer-thick ice sheets that covered much of Canada 20,000 years ago.

Simms and his colleagues compiled existing elevation measurement data from more than two dozen sites ranging from mid-Oregon to Baja, California. They then recalculated uplift rates for each, applying a correction for glacio-isostatic adjustment. Some areas are affected to a greater degree than others. The uplift rate for Punta Cabras in Baja, California showed the largest difference: 72 percent lower than previous estimates. The rate for the San Diego area was reduced by 62 percent. For other areas, the rate changes were not as dramatic. “Areas in Oregon are moving so fast that you add the correction, the adjustment is much smaller: 10 percent to 20 percent”, Simms said. “If a site is going up 100 meters versus 90 meters, that’s not a big change.

Here, sea level changed differently because of the distance from where these big ice sheets used to be.” The study provides one of the first spatially corrected sea level records for California. “A 2012 study looked at one spot with one model, but we looked at variation across the state”, Simms explained. “Now, our data can be applied not only in California but along the Pacific coast of North America.”

Plate Tectonics is the theory that the outer rigid layer of the earth (the lithosphere) is divided into a couple of dozen “plates” that move around across the earth’s surface relative to each other, like slabs of ice on a lake. Plates are a combination of continents and ocean basins. A plate may be an ocean basin alone or a continent alone or a combination of both. The essence of plate tectonic theory is that the plates slide around over the earth’s surface interacting as they do, at the plate boundaries.

The conclusion of the matter is that, along with the challenge of climate change, humanity is faced with a clear and present danger and, unless concrete steps are taken, the environment may not be this friendly afterwards. It is gratifying however, that the world is working round the clock to checkmate this challenge, one that faces Nigeria in equal measure. It is disheartening to note that Nigeria is allowing herself tolag behind in the race! The position paper the world expects from Nigeria on the concrete steps she’s taking along these lines is yet to be submitted as at the time of going to press.

What is so difficult in putting an end to gas flaring, regulate the inflow of junk cars and increase power generation to reduce the menace of generator fumes among others? This is a direct challenge to the climate change department of Nigeria’s ministry of environment! It is a challenge to the leadership and followership in Nigeria. Taking up the challenge is the only way to contain the threat, the only way to save ourselves from ourselves!
• Kayode Adeoye is an oil and gas expert from Lagos.

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