Islamic banks adhere to the concepts of Islamic law. This form of banking revolves around several well-established principles based on Islamic canons. Banking crises have developed many times throughout history when one or more risks have emerged for a banking sector as a whole. Prominent examples include the bank run that occurred during the Great Depression, the U.S. Savings and Loan crisis in the 1980s and early 1990s, the Japanese banking crisis during the 1990s, and the sub-prime mortgage crisis in the 2000s.Banks can create new money when they make a loan. New loans throughout the banking system generate new deposits elsewhere in the system. The money supply is usually increased by the act of lending, and reduced when loans are repaid faster than new ones are generated. In the United Kingdom between 1997 and 2007, there was an increase in the money supply, largely caused by much more bank lending, which served to push up property prices and increase private debt. The amount of money in the economy as measured by M4 in the UK went from £750 billion to £1700 billion between 1997 and 2007, much of the increase caused by bank lending. If all the banks increase their lending together, then they can expect new deposits to return to them and the amount of money in the economy will increase. Excessive or risky lending can cause borrowers to default, the banks then become more cautious, so there is less lending and therefore less money so that the economy can go from boom to bust as happened in the UK and many other Western economies after 2007.All banking activities must avoid interest, a concept that is forbidden in Islam. Instead, the bank earns profit (markup) and fees on the financing facilities that it extends to customers.