New Orleans was vulnerable to flooding even before the city's footprint departed from the natural high ground near the Mississippi River. In the late 20th century, however, scientists and New Orleans residents gradually became aware of the city's increased vulnerability. In 1965, flooding from Hurricane Betsy killed dozens of residents, although the majority of the city remained dry. The rain-induced flood of May 8, 1995, demonstrated the weakness of the pumping system. After that event, measures were undertaken to dramatically upgrade pumping capacity. By the 1980s and 1990s, scientists observed that extensive, rapid, and ongoing erosion of the marshlands and swamp surrounding New Orleans, especially that related to the Mississippi River–Gulf Outlet Canal, had the unintended result of leaving the city more vulnerable than before to hurricane-induced catastrophic storm surges.