became part as the second article of the 1818 treaty declared the 49th parallel to be the official border between the U.S. and Canada up to the Rocky Mountains. (This borderline was extended to the Pacific Ocean in 1846 under the Oregon Treaty.) The land acquired under the treaty had an area of , comprising 1.3 percent of total U.S. land area. Centered on the Red River of the North, these lands had previously been under the control of Great Britain. West of the Red River Valley, the territory of the Louisiana Purchase, which the US acquired from France, extends north of the 49th parallel. The US ceded this to Britain in exchange for gaining the Red River Valley. These northernmost parts of the Louisiana Purchase are one of the few North American territories ever ceded by the United States to a foreign power. Prone to flooding The four factors make the Red River Valley so prone to flooding (the factors are related to physical geography): Synchrony of Discharge with Spring Thaw: The Red River flows northward. The spring thaw also proceeds gradually northward. As a result, runoff from the southern portion of the valley gradually joins the fresh melt-off waters from northerly areas along the Red River. In the northern part of the Valley, this can result in devastating floods if the effects occur at the same time. Ice Jams: These are also produced because of the northward-flowing river system. Ice is moving from the southern Valley and freshly-broken ice is moving from the central and northern Valley. These two meet steadily; as a result, ice concentration in this system builds and causes delay of water flow. Glacial Lake Plain: The floor of Glacial Lake Agassiz is one of the flattest expanses of land in the world. Here, the Red River has cut a shallow, winding valley. As a result of this, when the river floods on this plain, a devastating event can occur. The areal coverage of the waters can become dramatic. Being approximately 9,300 years old, the Red River has not yet carved a large valley-floodplain systems on the surrounding geography. Thus, the large lake plain becomes the floodplain to the Red River. The Lake Agassiz glacial lake plain extends around 100 miles from east to west, end to end, between northeastern North Dakota and northwestern Minnesota. Decrease in Gradient Downstream: The gradient, or slope, of the