Umnak was to be an outpost in a new area of dominance that would later include the Samoan and Fiji Islands and New Caledonia. The Japanese were unaware of the covert preparations being made by the United States as they believed that the island was only protected by a few ships operating in Aleutian waters. Geography and climate Umnak, the third largest of the Aleutian Islands after Unimak and Unalaska, lies in the Fox Islands of the Aleutian Islands of the Bering Sea, to the southwest of the larger island of Unalaska. It is approximately in length () and wide on average. The island was separated in the last glacial period and now lies about from North American shores. It is an active volcanic island, with a land area of and with a coast line extending over . The elevation of the island is . The island is very mountainous with a low level of vegetation. The island does not have a harbor, although a sizeable bay is located in western part of the island and contains the Adugak Island. The southern point of the island is known as Cape Sagak. The highest peak of the island, the Mount Vsevidof stratovolcano, is located in the southwestern part of the island. Its symmetrical cone rises abruptly from its surroundings and forms a crater at a height of . Its most recent eruption was caused by an earthquake on March 9, 1957. The mountain erupted on March 11, 1957, and the eruption ended the next day. To the east of Mount Vsevidof is the Russian Bay valley and another stratovolcano, Mount Recheshnoi which is also deeply dissected with a height of . In the southwest is the settlement of Nikolski further south and a lake, Umnak Lake, to its southeast which is just over in length. The ancient settlement of Chaluka is located between this lake and Nikolski. This area is known as the Samalga Pass and was the center of ancient activity on the island and is located about off the southwestern tip of the island (Cape Sagak). The north-northeastern part of the island contains tholeiitic basaltic rocks and is characterized by tension faulting, lava flows and fragmental deposits of igneous rocks. The volcano of Mount Okmok, characterized by its wide circular caldera, it located in the northwestern part of the island. This generally flat central basin has an average elevation