Abstract

The
frequency of natural disasters across the world has been increasing drastically
throughout recent times, with intense hurricanes taking the lead as one of the
most devastating forces of nature.  This
paper explains the relationship between intense hurricane landfalls and coastal
sedimentary deposits, and further describes the methods scientists use to
determine prehistoric hurricane characteristics.  5 scholarly sources were used to explain the
three main points covered and were accompanied by 2 scientific websites that
were used to explain the basics of hurricanes. 
Intense hurricanes are classified as any one that reaches and/or exceeds
category 3 on the Saffir-Simpson scale, with sustained winds of 111-129 mph (Hurricane, n.d.).  The frequency and time period of intense
hurricane landfalls can be determined using backbarrier sedimentary evidence
via core samples and radiocarbon dating techniques (Donnelly et al., 2001a).  The data gathered by the technique of extracting
core samples and dating them can be useful in determining the history of
intense hurricane landfalls in an area, and these discoveries can help
scientists predict the likelihood of an intense storm making landfall again in
the future.  Additionally, these methods
can be used to make conclusions on which periods of time experienced high and
low intense storm frequency (Donnelly et al., 2001b).  Relationships can be drawn that explain what
environmental characteristics effected the trends most and why each period
experienced such trends.  Finally,
sedimentary evidence can be used to describe the correlations between intense
hurricane landfall frequency over large areas, such as oceanic masses.  This is useful when trying to determine
whether intense storms were only common in one area, or instead across larger
distances (Scileppi & Donnelly, 2007). 
Overall, this paper explains the significance of sedimentary evidence
when analyzing the history and future of intense hurricane landfall, and
provides valuable information regarding the tools and methods scientists use to
explain weather trends.

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Keywords: hurricane, backbarrier,
radiocarbon dating, core sample

 

 

 

 

Sedimentary Deposits’ Relationship
to the Past and Future of Hurricanes

In
a world plagued by a rapidly increasing frequency of natural disasters, some
reign mightier than others, with the hurricane topping the list in terms of
destructive capability and power.  Hurricanes,
also known as tropical cyclones, are rapidly rotating storm systems with
low-pressure centers, strong winds, and a spiral arrangement of thunderstorms
that produce extreme amounts of rain in a short period of time.  These storms can grow to over 1,350 miles
wide, typically form over large bodies of warm water, and begin rotating
towards the equator due to the Coriolis effect, or spin of the earth (Hurricanes, 2015).  Their strength is separated into five
different categories of increasing violence based on the Saffir-Simpson scale,
with category 1 hurricanes having 74-95 mph sustained winds and category 5
hurricanes seeing winds in excess of 157 mph. 
When a storm reaches the ranking of category 3, it is considered an
intense hurricane, with winds of 111-129 mph and the capability to destroy
islands, coastlines, and even inland features (Hurricane, n.d.).  Hurricanes
have been forming and wreaking havoc on the world’s coastlines since the dawn
of time, so understanding them and their formation is critical when attempting
to predict them in the future.  Historical
records of these massive, rotating storms only give those studying them a few
hundred years of data to work with, but the geological evidence of intense
hurricanes can give researchers a much larger time frame to analyze.  While historical records often only go back
370 years, sedimentary core samples, aerial photographs, and radiocarbon dating
can be used to analyze a time period’s hurricane activity thousands of years in
the past.  These samples can be gathered,
radiocarbon dated, and analyzed by researchers in order to establish the
probability of intense hurricane landfalls happening each year, which can help
researchers better predict future hurricanes (Donnelly, et al., 2001a).  Additionally, the use of sedimentary evidence
can yield information that shows what caused different variances in hurricane
frequency throughout specific time periods in history (Liu & Fearn, 2000).  Finally, the data collected from radiocarbon
dating sedimentary samples in one area can be compared to similar samples in
another area, where conclusions can be drawn on a time period’s hurricane
activity over large areas (Scileppi & Donnelly, 2007).  Sedimentary deposits are a valuable tool in
analyzing prehistoric intense hurricane landfalls, and can give scientists an
idea of when a hurricane made landfall, the intensity of the hurricane at that
time, the conditions the hurricane formed under, and the probability of a
similar storm occurring again.

When
investigating the past activity of hurricanes, one will find that modern
equipment has only helped the National Oceanic and Atmospheric Administration
record into the late nineteenth century, and historical records typically only
date a maximum of 130-370 years into the past (Donnelly et al., 2001a).  When glancing at the global geological
timeline, these 370 years of the earth’s 4.54 billion years of history is
extremely insignificant, making it crucial for researchers to be able to look
further into the past to draw valid conclusions.  To extend the observation periods for
research, sediment cores can be drawn from back-barrier areas and radiocarbon
dated to find a range of dates of deposition. 
Back-barrier areas are located between barrier islands and the mainland
and can consist of bodies of water such as bays, lagoons, and marshes (Donnelly
et al., 2001a).  When an intense
hurricane occurs, strong storm surges can overtop the barrier island, removing
sediment from beaches and nearshore environments and depositing the sediments
in overwash fans across the back-barrier areas. 
These sediment depositions are then preserved, and when cores are
extracted, the sediments in each overwash layer can be dated to their
respective time period of deposition (Donnelly et al., 2001a).  Often times, researchers will use aerial
photographs of recorded storms to match the sediments to specific storms, and
when this occurs, they can begin to look further back, often in excess of 2,000
years, and speculate when intense hurricanes struck an area and how strong the
hurricanes were.  In a study conducted by
Jeffrey Donnelly at Brown University in 2001, a team of researchers collected
14 core samples from the Succotash salt marsh in East Matunuck, Rhode Island,
and used these samples accompanied by recorded aerial photographs and data to
analyze the intense hurricane history of the study area (Donnelly et al.,
2001a).  Initially, the two historically
recorded overwash fans were discovered in the stratigraphic record and linked
to intense hurricanes in 1954 and 1938, but an additional four large-scale fans
were found to be deposited in the marsh sediments as well.  Of the six total fans the team found, four of
them were deposited in recent history, and were determined to be the result of
storms in 1954, 1938, 1815, and 1638 or 1635. 
The two remaining overwash fans were prehistoric, with no recorded data
of intense hurricanes at the time of deposition.  Through radiocarbon dating, the team found
that the prehistoric fans were deposited in two time periods between 1295-1407
and 1404-1446 and were most likely the result of intense hurricane
landfall.  Based on the sedimentary core
samples gathered, the correlation of the fans to recorded storms, and the
radiocarbon dating of the prehistoric deposits, Donnelly and his team were able
to conclude that a total of 7 intense hurricanes struck the Southern Rhode
Island coast in the past 700 years (Donnelly et al., 2001a).  By doubling the time period of study from
what was recorded, this team of researchers was able to discover two additional
intense hurricanes that were not previously recorded.  Although doubling the time frame of what was
previously recorded is taking a step in the right direction, this method has
much more potential, as shown by Kam-biu Liu in a study that looked 7,000 years
into the past in order to draw conclusions on coastal environmental changes and
catastrophic hurricane landfalls (Liu & Fearn, 2000).  In addition to looking into the past of
intense hurricane landfalls, sedimentary deposits can help researchers look
into the future as well.  When scientists
know how many intense storms occurred over a long period of time, they can
calculate the probability of a similar intense hurricane happening each year,
by dividing the total number of intense storms in the time period by the number
of years the research encompassed (Donnelly et al., 2001b).  In another study conducted by Jeffrey
Donnelly and his research team from Brown University, the focus was turned on
the number of intense hurricane strikes that effected the Southern New Jersey
coast in the last 700 years.  His team
collected nine samples and found three historic and prehistoric overwash
deposits associated with intense storms over a 700 year period.  Of those three intense storms, two were
determined to be intense hurricanes with the third being the Ash Wednesday
northeaster which occurred March 5-8, 1962. 
By knowing the total number of intense hurricanes that made landfall in
Southern New Jersey in the last 700 years, Donnelly’s team concluded that the
annual landfall probability for the area was 0.3%, meaning that one landfall is
probable every 350 years (Donnelly et al., 2001b).  Calculating the probability of an intense
storm landfall is relatively simple, and is done by dividing the number of
intense storms by the number of years in the study period, and lastly
multiplying the result times 100 to change the figure into a percentage.  Hypothetically, if there were 7 intense
hurricane landfalls in an area over the course of 1,300 years, the probability
of a similar storm making landfall would be calculated by:

This probability figure
of .539% means that every year, this certain study area has a .539% chance of
an intense hurricane making landfall.  Using
methods like these, researchers and meteorologists can better prepare for
storms and gain a greater understanding of the frequency of intense hurricane
landfall in a particular area.  The use
of data to predict probability is another reason why the use of radiocarbon
dating in sedimentary core samples can be valuable when both analyzing past
storms as well as predicting future ones.

Another
use of sedimentary evidence when investigating hurricanes is identifying time
periods of hurricanes and analyzing what climatic factors influenced the
specific period.  When investigating the
past intense hurricane activity in a certain area, sedimentary core samples and
carbon dating can also be used to identify times of frequent hurricanes and
times when there weren’t so many hurricanes (Liu & Fearn, 2000).  In a study performed by Kam-biu Liu and
Miriam L. Fearn of Lousiana State University and the University of South
Alabama, sediment cores were taken from Western Lake, FL and used to provide a
7,000 year record of coastal environmental changes and catastrophic hurricane
landfalls along the Gulf Coast.  Using
the sedimentary record provided by various core samples from the lake, the pair
concluded that there were few intense hurricanes during the periods of 5000-3400
years ago and 1000 years ago to present. 
Oppositely, it was determined that a period of frequent, intense
hurricane landfalls occurred between 3400 and 1000 years ago.  These assumptions were drawn based on the
overwash sediment depositional layers in the lake combined with radiocarbon
dating of the samples.  From their
research, Liu and Fearn concluded that the fluctuations in hurricane frequency
and intensity were related to shifts in the positions of the Jet Stream and
Bermuda High, instead of changes in climate (Liu & Fearn, 2000).  This information can be useful in
understanding the origins of these storms, what causes them, and can also help
scientists better understand how changing climate affects the severity and
frequency of intense hurricanes.  It has
long been proposed that hurricane frequency is directly related to the increase
in surface water temperatures in the ocean, but some scientists refute this
proposal, claiming that instrumental record is too short and inconsistent to
show definitive trends in data. 
Sedimentary core samples can be used to study the correlations between
climatic conditions and hurricane activity on substantially longer time scales
than instrumental record can show, allowing researchers to determine what
climatic factors influence hurricane formation and frequency the most (Donnelly
& Woodruff, 2007).  In a study
conducted by Jeffrey Donnelly and Jonathan Woodruff, the pair looked more into
the relationship between climate and intense hurricanes by researching 5,000
years of intense hurricane activity based on sedimentary deposits from a
Caribbean lagoon.  Core samples of
sedimentary deposits in the lagoon were extracted and radiocarbon dated so that
the two researchers could formulate a historical timeline pertaining to intense
hurricane landfall.  They found that
intense hurricane landfall has varied throughout the last 5,000 years on
centennial to millennial scales, which triggered the pair to dig further into
the data.  When the sediment record was
compared to the paleo-climate records, it was determined that intense hurricane
landfall frequency was not varied by climate change, but instead by variances
in atmospheric conditions.  The two
influential atmospheric dynamics Donnelly and Woodruff found to be causing the
variances were the El Niño current and the varying strength of the West African
monsoon.  They concluded that sea surface
temperatures as high as ones in the present day are not necessary to support
periods of increased intense hurricane frequency, and that in order to
accurately predict changes in hurricane frequency, it is crucial to understand
atmospheric dynamics such as the El Niño and West African monsoon (Donnelly
& Woodruff, 2007).  Research and
conclusions encompassing the climatic conditions that have historically caused
increases and decreases in intense hurricane landfall frequency are yet another
valuable result of using sedimentary evidence to analyze intense storm
action.  The relationships between
hurricanes and climate are of special importance in the present day considering
that the Earth is experiencing a warming period faster than ever before.  By understanding the effects of climate on
past intense storm systems, scientists can better understand why patterns of
intense storm landfall are increasing in the present day.

Finally,
sedimentary evidence can be used to discover correlations between different strong
hurricane landfalls over large areas such as oceans, but only when similar data
is collected and compared from the separate study areas.  When data is used in this way, the similarities
and differences in climatic and storm characteristics can be explained between
different coastal points that share the same oceanic mass, and conclusions can
be drawn regarding the intense hurricane activity in that specific ocean per
unit time (Scileppi & Donnelly, 2007). 
This data is particularly useful when trying to understand the overall
presence of intense hurricanes in an area throughout a specific period.  The process begins when sedimentary core
samples are taken and analyzed, where researchers are looking for evidence of
overwash fans and attempting to link these sedimentary deposits to specific
time periods via radiocarbon dating. 
From here, researchers can further make conclusions on what time periods
contained high or low hurricane frequency, and link these conclusions to
specific climatic events or cycles.  Once
all of the data is acquired and overall conclusions are drawn based on one
specific coastal point, similar records of data can be pulled from different
coastline points that share the same ocean, and comparison can begin to take
place (Scileppi & Donnelly, 2007).  Often,
similarities are seen in the data from different areas, which helps researchers
gain a better understanding of the consistency of hurricanes as well as what
causes the different cycles of high and low storm frequencies.  One specific study conducted by Elyse
Scileppi and Jeffrey Donnelly used overwash deposits, radiocarbon dating, and
documented data to analyze the correlation between intense hurricane landfalls
in New York City, the Gulf Coast, and the Caribbean coast.  They began their study by recovering evidence
of strong hurricane landfall in the New York City area from historical records,
and furthered their investigations by looking for evidence of prehistoric storm
landfall in the backbarrier sediments of the area.  The pair found that the overwash deposits in
the area were related to the documented landfalls of the area’s most intense
hurricanes in 1893, 1821, 1788, and 1693. 
They also found a large gap in the frequency of intense hurricane
landfall in the area that started directly before recorded history began, and
concluded based on sedimentary evidence from multiple sites, that a period of
infrequent intense storm landfall possibly occurred between 900 years ago and
250 years ago (Scileppi & Donnelly, 2007). 
Adding to these findings, their research found that the lower sea
surface temperatures caused by the back end of the Little Ice Age did not deter
intense storm landfall.  Instead of a
decrease in landfall with lower sea surface temperatures than today, the area
experienced an increase in overall intense hurricane landfall.  When the team compared their research
findings to findings from similar studies performed in different areas, they
were able to conclude that intense hurricane landfalls in the New York City
area were roughly synchronous with similar landfalls observed on the Caribbean
Coast and Gulf Coast.  Finally, they
determined that the changes in landfall frequency were experienced across the
North Atlantic Ocean instead of just at their research site of the New York
City area (Scileppi & Donnelly, 2007). 
Studies like the one conducted by this research pair are crucial when
attempting to understand the relationship between environmental factors and
intense storms, and they can often illustrate different trends experienced in
prehistoric eras.  By understanding how
the trends in data such as climate, sea surface temperatures, and sea level
relate to intense hurricane landfall, meteorologists and scientists can not
only better understand the environmental factors of the past, but can also draw
relationships to the present and future. 
As sea level trends and climate continue to change, it is of the utmost
importance for the science community and coastal population to understand how
the frequency of intense storm landfall will change.

In
conclusion, sedimentary evidence can be an extremely powerful tool to use when
analyzing the past, present, and future of intense hurricane landfall.  Core samples from backbarrier areas coupled
with radiocarbon dating techniques can reveal an overwhelming amount of
information about hurricane landfalls, and specifically about those that
occurred far before the beginning of recorded history.  Since recorded history only goes back about
370 years, there are no documents or evidence of hurricane landfalls before
this point in time, so sedimentary evidence is often the only proof available
that intense storm landfall occurred at all (Donnelly et al., 2001a).  Researchers can use this sedimentary evidence
to analyze prehistoric storm landfalls, and they can further use it to better
predict hurricanes moving into the future. 
Also, sedimentary evidence can be used to estimate time periods of frequent
intense storm landfall as well as periods of lower frequency storm landfall
(Donnelly et al., 2001b).  This is also
important when attempting to draw relationships between past conditions and
present ones moving into the future. 
Finally, sedimentary evidence can be used to form relationships between
different locations of landfalls spread out across large areas such as oceanic
masses.  This is done by using similar
research methods at different locations and then comparing data and conclusions
in search of a correlation between the locations.  If data is relatively synchronous between the
different locations, it can be concluded that the entire area had experienced
higher or lower than normal intense storm landfall, instead of just one
specific location.  From here, researchers
can make conclusions as to what climatic conditions were occurring at the time
and how they relate to the formation and landfall of intense storms (Scileppi
& Donnelly, 2007).  Overall,
sedimentary deposits are a valuable tool in analyzing prehistoric intense
hurricane landfalls, and they can help give scientists and researchers a
detailed outline of when a hurricane made landfall, how intense it was, the
climatic conditions the earth was experiencing at the time, and the probability
of a similar storm occurring in the near or distant future.

 

 

References

(2015).  Hurricanes: Science and Society.  Retrieved from http://www.hurricanescience.org/science/science/hurricanestructure/

Donnelly, J.P., Bryant, S.S., Butler, J., Dowling,
J., Fan, L., Hausmann, N., . . . Webb III, T. (2001).  700 yr sedimentary record of intense
hurricane landfalls in Southern New England. 
Geological Society of America, 113(6), 714-727.

Donnelly,
J.P., Roll, S., Wengren, M., Butler, J., Lederer, R., Webb III, T. (2001).  Sedimentary evidence of intense hurricane
strikes from New Jersey.  Geological Survey of America, 29(7), 615-618.

Donnelly,
J.P., Woodruff, J.D. (2007).  Intense
hurricane activity over the past 5,000 years controlled by El Niño and the West
African monsoon.  Nature Publishing Group, 447, 465-468. 
https://www.researchgate.net/publication/6309528

Liu,
K.B., Fearn, M.L. (2000).  Reconstruction
of Prehistoric Landfall Frequencies of Catastrophic Hurricanes in Northwestern
Florida from Lake Sediment Records.  Quaternary Research, 54(2), 238-245.

Scileppi,
E., Donnelly, J. P. (2007).  Sedimentary
evidence of hurricane strikes in western Long Island, New York.  Geochemistry
Geophysics Geosystems, 8(6), 1-25.

The
Columbia Encyclopedia, 6th ed. 
Hurricane.  Retrieved from http://www.encyclopedia.com/earth-and-environment/atmosphere-and-weather/weather-and-climate-terms-and-concepts/hurricane