Credit: NOAA The Deepwater Horizon oil spill is the largest marine oil spill in history, and was caused by an explosion on the Deepwater Horizon offshore oil platform about 50 miles southeast of the Mississippi River delta on April 20, 2010. Most of the 126 workers on the platform were safely evacuated, and a search and rescue operation began for 11 missing workers. The Deepwater Horizon sank in about 5,000 feet (1,500 m) of water on April 22, 2010. On April 23 the U.S. Coast Guard suspended the search for missing workers who are all presumed dead. After a series of failed efforts to plug the leak, BP said on July 15 that it had capped the well, stopping the flow of oil into the Gulf of Mexico for the first time in 86 days. The BP spill is by far the world's largest accidental release of oil into marine waters. The U.S. goverment estimated that about 4.9 million barrels of oil were released, of which about 800,000 barrels were captured by containment efforts.
Ixtoc. Credit: NOAA The second-largest largest oil spill in North America occurred in the Gulf of Mexico. The 200-foot-deep exploratory well, Ixtoc I, blew out on June 3, 1979, in the Bay of Campeche, Mexico, releasing 10,000 - 30, 000 barrels (0.4 - 1.2 million gallons) per day for nine months. Nearly 500 dispersant air sorties were flown in Mexico. Manual cleanup in Texas was aided by storms. Though the blowout preventer (BOP, valve designed to seal off a wellhead) failed, injection of metal and concrete balls into the well slowed the release. By the time the well was brought under control in March 1980 by drilling two relief wells to relieve pressure, an estimated 113 million to over 300 million gallons of oil had spilled (10 times the amount of oil spilled by the Exxon Valdez). Oil travelled 800 miles to the north, oiling more than 150 miles of shoreline in Texas and unknown miles of shoreline in Mexico.
Oil spill in the aftermath of Hurricane Katrina. Credit: NOAA More than 250 oil-related pollution incidents were reported in the wake of Hurricane Katrina, releasing an estimated total of 8 million gallons of oil directly into inland waterways and wetlands. Because many spills went unreported and others were never attributed to a specific source, the actual amount of oil released into the environment will never be known. Shallow nearshore areas, coastal and inland wetlands, and sand beaches were among the numerous habitats impacted by these spills. A variety of cleanup methods were employed including in-situ burning, mechanical cleanup (heavy equipment, vacuuming, etc.), and manual recovery and removal of oil. However, many marsh areas were left to recover naturally because the impacts associated with cleanup of the oil would have exacerbated damage to these sensitive marsh environments.
Burmah Agate. Credit: NOAA On November 1, 1979, the M/V Burmah Agate collided with the freighter Mimosa southeast of Galveston Entrance in the Gulf of Mexico. The collision caused an explosion and fire on the Burmah Agate that burned until January 8, 1980. An estimated 2.6 million gallons of oil were spilled, and an estimated 7.8 million gallons were consumed by the fire. Oil traveled more than 200 miles, impacting Matagorda Peninsula and Padre Island. Marshes were not cleaned because response efforts could have caused more damage than the oil.
Megaborg. Credit: NOAA The Megaborg released 5.1 million gallons of oil as the result of a lightering accident and subsequent fire. The incident occurred 60 nautical miles south-southeast of Galveston, Texas on June 8, 1990. Most of the released oil burned during the initial response. Once the fire was controlled, an oil slick formed and began to spread to the north-northwest of the site. A cadre of volunteers was mobilized to help with cleanup efforts, but little shoreline oiling resulted from this spill. Calm seas and warm weather aided off-shore skimming activities and increased evaporative losses of the oil. A small portion of the slick was also effectively treated with dispersants. The oil slick weathered and degraded into tarballs. The fate of these tarballs is unknown, but they were not seen on beaches that were monitored.
Alvenus. Credit: NOAA On July 30, 1984, T/VAlvenus grounded in the Calcasieu River Bar Channel southeast of Cameron, Louisiana, spilling 65,500 barrels (2.7 million gallons) of Venuzuelan crude oil into the Gulf of Mexico. Oil travelled more than 100 miles to the west, where it came onshore on the Bolivar Peninsula and entered Galveston Bay. The oil smothered marine life attached to groins and sea walls, but despite the presence of thousands of birds on sand islands, few were injured. A large amount of oiled sand was removed.
Ocean 255. Credit: NOAA On August 10, 1993, three ships collided in Tampa Bay, Florida: the BOUCHARD B155 barge, the freighter BALSA 37, and the barge OCEAN 255. The BOUCHARD B155 spilled an estimated 336,000 gallons of No. 6 fuel oil into Tampa Bay. Nearby sand beaches, mangrove islands, oyster and seagrass beds, tidal mudflats, jetties, seawalls, and riprap were extensively oiled. On sand beaches, surface oiling high on the beach was removed manually. Buried oil on sand beaches was removed with heavy equipment, and oil-stained sands were surfwashed. Tarmats in the mangroves, oyster and seagrass beds, and tidal mudflats were primarily removed by vacuuming. Seawalls within the bay were cleaned using high-pressure hot-water washes.