Great Famine, also called Irish Potato Famine, Great Irish Famine, or Famine of 1845–49, famine that occurred in Ireland in 1845–49 when the potato crop failed in successive years. The crop failures were caused by late blight, a disease that destroys both the leaves and the edible roots, or tubers, of the potato plant. As a direct consequence of the famine, Ireland's population fell from almost 8.4 million in 1844 to 6.6 million by 1851. About 1 million people died and perhaps 2 million more eventually emigrated from the country. Many who survived suffered from malnutrition. Additionally, because the financial burden for weathering the crisis was placed largely on Irish landowners, hundreds of thousands of tenant farmers and laborers unable to pay their rents were evicted by landlords unable to support them. Continuing emigration and low birth rates meant that by the 1920s Ireland's population was barely half of what it had been before the famine.
Dense water sinks below less dense water. This is the principle that drives the deep ocean currents that circulate around the world. A combination of high salinity and low temperature near the surface makes seawater dense enough to sink into the deep ocean and flow along the bottom of the basins.
