Robert E. Lucas and Nancy L. Stokey have a lovely readable article in the June 2011 issue of The Region, published by the Federal Reserve Bank of Minneapolis, on "Liquidity Crises." The paper offers a readable overview that connects the main  themes of high-profile academic theory papers in this area to what actually  happened. A few highlights:
"Any one bank, no matter how large and respected, can go out of  business  almost without a ripple. Anyone living in an American city can list   the downtown banks he grew up with that vanished in the merger movement  of the  1990s. Who misses them? Indeed, who misses Lehman Brothers, for  generations one  of the most respected financial institutions in the  world? Its valuable assets,  both physical and human capital, were  quickly absorbed by surviving banks  without notable loss of services.  It was the signal effect of the Lehman  failure, whether a signal about  the situations of private banks or about the  Federal Reserve’s  willingness to lend to troubled banks, that triggered the  rush to  liquidity and safety that followed."
"We will argue  here that what happened in September 2008 was a kind of  bank run. Creditors of  Lehman Brothers and other investment banks lost  confidence in the ability of  these banks to redeem short-term loans.  One aspect of this loss of confidence was  a precipitous decline in  lending in the market for repurchase agreements, the  repo market.  Massive lending by the Fed resolved the financial crisis by the  end of  the year, but not before reductions in business and household spending   had led to the worst U.S. recession since the 1930s."
"As deposits moved out of commercial banks,  investment banks and money  market funds increasingly provided close substitutes  for the services  commercial banks provide. Like the banks they replaced, they  accepted  cash in return for promises to repay with interest, leaving the option   of when and how much to withdraw up to the lender. The exact form of the   contracts involved came in enormous variety. In order to support these   activities, financial institutions created new securities and new  arrangements  for trading them, arrangements that enabled them  collectively to clear ever  larger trading volumes with smaller and  smaller holdings of actual cash. In  August of 2008, the entire banking  system held about $50 billion in actual cash  reserves while clearing  trades of $2,996 trillion per day. Yet  every one of these trades involved an uncontingent promise to pay  someone hard cash  whenever he asked for it. If ever a system was  “runnable,” this was it. Where  did the run occur?"
Lucas and Stokey answer that the run occurred in repo markets, and offer an intriguing table that shows while cash, private demand deposits, and money market funds all  had more money in January 2009 than they had in January 2008, repo contracts held by primary dealers dropped substantially.
 
