Short answers, pulled from the story.
The 1998 Russian financial crisis was caused by a combination of factors: a chronic fiscal deficit worsened by the estimated $5.5 billion cost of the First Chechen War, declining oil and commodity prices following the 1997 Asian financial crisis, a high fixed exchange rate the Central Bank spent approximately $27 billion defending, and the government's inability to collect sufficient tax revenue to cover monthly debt interest payments.
Russia defaulted on its domestic debt on the 17th of August 1998, when the government and Central Bank issued a joint statement devaluing the ruble, restructuring state securities including GKOs and OFZs, and imposing a 90-day moratorium on certain bank obligations.
The ruble lost approximately two-thirds of its value within a month of the default. On the 14th of August 1998 it stood at 6.29 rubles per US dollar; by the 21st of September 1998 the rate had reached 21 rubles per dollar after the Central Bank abandoned its floating peg policy on the 2nd of September.
Yevgeny Primakov became prime minister, approved by the State Duma by an overwhelming majority on the 11th of September 1998. Yeltsin had first fired Sergei Kiriyenko on the 23rd of August and attempted to restore Viktor Chernomyrdin, but the Duma rejected Chernomyrdin twice before Primakov was nominated.
Russian inflation reached 84 percent in 1998, and welfare costs grew considerably. Several major banks closed, including Inkombank, Oneximbank, and Tokobank. Bankers Trust survived only by being acquired by Deutsche Bank for $10 billion in November 1998.
Russia recovered faster than most observers expected, driven primarily by rapidly rising world oil prices in 1999 and 2000, which produced large trade surpluses. Domestic industries, particularly food processing, also gained from the ruble's devaluation because it made imported goods sharply more expensive. The widespread use of barter in the Russian economy also reduced the crisis's impact on producers who had never fully relied on the banking system.