Journal of Coastal Research
SI
85
841–845
Coconut Creek, Florida
2018
Multi-proxy Characterization of Hurricanes Rita and Ike Storm Deposits in the Rockefeller Wildlife Refuge, Southwestern Louisiana Qiang Yao†*, Kam-biu Liu †, and Junghyung Ryu† †
Department of Oceanography and Coastal Sciences Louisiana State University Baton Rouge, Louisiana 70803, U.S.A.
www.cerf-jcr.org
ABSTRACT Yao, Q.; Liu, K.-B., and Ryu, J., 2018. Multi-proxy Characterization of Hurricane Rita and Ike Storm Deposits in a Coastal Marsh in the Rockefeller Wildlife Refuge, Southwestern Louisiana. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 841–845. Coconut Creek (Florida), ISSN 0749-0208. www.JCRonline.org
In 2005 and 2008, Hurricanes Rita and Ike made landfalls as category 3 and 2 hurricanes to the west of Rockefeller Wildlife Refuge (RWR) in southwestern Louisiana. In 2013, three ~30 cm sediment monoliths dominated by brown clay were recovered along a ~30 m transect perpendicular to the shoreline from the RWR. Each monolith contains two distinct light-colored calcareous storm deposits that are attributable to these two landfalling hurricanes. Loss-onignition and X-ray fluorescence (XRF) analyses were performed on all three sediment monoliths to study the sedimentological and geochemical characteristics of these two storm deposits. The geochemical results show that the storm deposits are characterized by higher-than-average values of Ca, Sr, Zr, and carbonates and low percentages of water and organics. In addition, remote sensing images show that the rate of average shoreline retreat at the RWR is ~14.5 m/yr from 1998 to 2017, and 19 m/year and 25.5 m/yr during the Hurricane Rita and Ike years, respectively. Both loss-on-ignition and XRF results also show that despite being a stronger storm, the Hurricane Rita layers are much thinner than those of Hurricane Ike in all monoliths. Remote sensing data support our interpretation that Hurricane Rita caused significant shoreline erosion and coastal recession in 2005, rendering the sampling locations at least 30 m closer to the ocean and thereby more susceptible to storm surges when Hurricane Ike struck in 2008. Thus, these results suggest that site-to-sea distance is an important factor in determining the thicknesses of storm deposits in coastal wetlands, particularly along shorelines undergoing rapid marine transgression. ADDITIONAL INDEX WORDS: Paleotempestology, storm deposits, coastal erosion, shoreline retreat, Hurricane Rita, Hurricane Ike, Rockefeller Wildlife Refuge, Louisiana
INTRODUCTION The coastal zones in Louisiana are frequently impacted by hurricanes. Instrumental records suggest that 53 hurricanes have made landfall near the coast of Louisiana since AD 1842. Among them, 16 were major hurricanes (category 3 to 5 on the SaffirSimpson Scale), an average return interval of ~11 years (NOAA, 2017). Recent studies suggest that hurricane storm surges can overtop beach barriers (Liu, 2004) and deposit large amounts of overwash sediment in low-lying coastal areas many km inland (Williams, 2011, 2012), and can cause significant shoreline erosion (Barras, Bernier, and Morton, 2008). Identification of storm overwash deposits in the coastal sedimentary records is an important way to determine how often such events occurred in the past. Such studies can give insights to the frequency, intensity, and dynamics of future hurricanes (Lane et al., 2011; Wallace et al., 2014). Empirical data on the sediment-stratigraphic characteristics of recent or historic hurricane deposits offer a means to identifying them in the geological record. However, ____________________ DOI: 10.2112/SI85-169.1 received 30 November 2017; accepted in revision 10 February 2018. *Corresponding author:
[email protected] © Coastal Education and Research Foundation, Inc. 2018
with few exceptions (Liu et al., 2011; Williams, 2011, 2012), such records are rare from the northern Gulf of Mexico coast in Louisiana. Here we present loss-on-ignition (LOI) and X-ray fluorescence (XRF) data of Hurricanes Rita and Ike storm deposits from a coastal marsh in the Rockefeller Wildlife Refuge (RWR), Southwestern Louisiana, to document their stratigraphic and geochemical characteristics. We also use remote sensing data to study the effects of these two hurricanes on shoreline erosion. METHODS Study Site Description The RWR is located in Cameron and Vermillion parishes on the Louisiana Gulf Coast (Fig. 1). The RWR occupies an elongated basin confined by the high Grand Chenier Ridge to the north and the low beach barriers to the south. Historically, extensive freshwater marsh grows near the Chenier ridge in the northern part of RWR; brackish marsh inhabits in the middle; and saltmarsh occupies areas close to the beach. The freshwater marsh vegetation consists primarily of graminoids, sawgrass (Cladium sp.), and cattail (Typha sp.). Vegetation in the lower two-thirds of the basin is dominated by Spartina sp., with wiregrass (Spartina patens) dominating the brackish marsh and hogcane (Spartina cynosuroides), iva (Iva frutescens), and oystergrass (Spartina
842 Yao, Liu, and Ryu
_________________________________________________________________________________________________ alterniflora) dominating the saltmarsh (Selman et al., 2011). This vegetation zonation pattern has been altered substantially over the past 40 years due to anthropogenic activities (Selman et al., 2011). The beach in RWR consists of primarily shell fragments that become coarser landward from the shoreline. Field observation reveals that very few clastic sediments were present along the beach. Succulent plant Batis maritima occupies extensive areas immediately adjacent to the beach. Three sediment monoliths were recovered from the succulent marsh. Each monolith contains 2 distinct light-colored calcareous sediment layers embedded in brown clay. These calcareous layers highly resemble overwash deposits caused by intense hurricanes (Liu, 2004).
category 3 hurricane with sustained winds of 190 km/h (NASA, 2017a). Because Rita made landfall almost immediately to the west of our study area, it caused catastrophic damages to the RWR (Fig. 2). The storm generated up to 5 m of storm surges and 25 cm of precipitation, resulting in widespread flooding and significant economic damages in coastal Louisiana. Hurricane Ike made landfall near Galveston, Texas on September 13, 2008 as a category 2 hurricane with sustained winds of 175 km/h (NASA, 2017b). Although Ike was over 100 km west of our study site when it made landfall, it had an extremely large eye, with eyewalls stretching from Galveston to Vermilion Bay, Louisiana, a distance of over 275 km (Fig. 2). Hurricane Ike brought 25-50 cm of precipitation and generated storm surges up to 6.8 m, causeing widespread flooding over 100 km of coastlines between Galveston Bay and southwestern Louisiana, including the RWR (NASA, 2017b) (Fig. 2).
Figure 1. location of the Rockefeller Wildlife Refuge (Huh, Walker, and Moeller, 2001) (a) and the three sediment monoliths (b).
Meteorological Data of Hurricane Rita and Ike Although our sediment monoliths captured two potential storm surge events, in recent years, five hurricanes made landfall close to our study area. They are Hurricanes Rita (cat 3, 2005), Humberto (cat 1, 2007), Ike (cat 2, 2008), Gustav (cat 2, 2008), and Isaac (cat 1, 2012). However, Hurricanes Humberto, Gustav, and Isaac likely did not cause significant overwash in our study area, because Humberto and Isaac are relatively weak hurricanes and Gustav made landfall to the east of RWR. Remote sensing images show clear evidence of storm surge-induced flooding and overwash fans on beaches across the RWR immediately after Hurricanes Rita and Ike (Figs. 2, 3). Based on the evidence, we attribute the 2 distinct calcareous sediment layers in our sediment monoliths to Hurricane Rita and Ike. As part of the record-breaking 2005 Atlantic hurricane season, Hurricane Rita was the 5th major hurricane of that year and 4th most intense Atlantic hurricane ever recorded in the Gulf of Mexico. On September 24, Rita made landfall in coastal areas between Sabine Pass, Texas and Holly Beach, Louisiana as a
Figure 2. Top-panel: satellite images of Hurricane Rita (NASA, 2017a) and Ike (NASA, 2017b). Mid- and bottom-panels: satellite images of RWR immediately before and after Hurricanes Rita and Ike. Red stars point to our study area.
Field Sampling In 2013, three ~30 cm sediment monoliths (ROC-1, ROC-2, and ROC-3) were recovered along a ~30 m transect perpendicular to the shoreline from the succulent marsh behind the beach in RWR. The first monolith, ROC-1 (29°40'11.9"N 92°51'01.5"W) was taken ~30 m behind the beach. ROC-2 (29°40'08.5"N 92°51'01.1"W) and ROC-3 (29°40'08"N 92°51'01"W) were taken at ~10 m and 20 m further toward the beach from ROC-1, respectively. The sediment monoliths were measured, photographed, and wrapped in the field, and stored in a cold room (4°C) at Louisiana State University. Laboratory Analyses Selected Google Earth satellite images of the study area were used to measure the shoreline erosion from AD 1998 to 2017 (Fig.
Journal of Coastal Research, Special Issue No. 85, 2018
843 Multi-proxy Characterization of Hurricane Rita and Ike Storm Deposits in the Rockefeller Wildlife Refuge
_________________________________________________________________________________________________ 3). The center point of our study transect was used as one fixed point. We drew a line perpendicular to the shoreline between this fixed point and another point at the outer (seaward) edge of the beach (the white area on satellite image) on every satellite image (the red lines on Fig. 3). These lines were used to measure the site-to-sea distance for when the satellite image was taken. The site-to-sea distance at different time intervals was used to calculate the rate of shoreline changes.
regression plot (F 50%) and organic matter (>10%) contents, while contents of carbonates (
