The ice-clogge waters of Antarctica's McMurdo Sound extend about 55 km (35 mi) long and wide. The sound encompasses 2,500 miles (4,000 kilometers) of shoreline which opens to the Ross Sea to the north. The Royal Society Range rises from sea level to 13,205 feet (4,205 m) on the western shoreline. The nearby McMurdo Ice Shelf scribes McMurdo Sound's southern boundary. Ross Island, an historic jumping-off point for polar explorers, designates the eastern boundary. The active volcano Mt Erebus at 12,448 feet (3,794 m) dominates Ross Island. Antarctica's largest science base, the United States' McMurdo Station, as well as New Zealand’s Scott Base are located on the island’s south shore. Less than 10 percent of McMurdo Sound's shoreline is ice-free.