A prolonged period of market calm has come to an abrupt halt on Wall Street.

The Dow Jones Industrial Average DJIA, -0.87% and the S&P 500 index SPX, -1.11% slipped below their short-term trading averages and went negative for the year, relinquishing gains of more than 5% in January in a span of a few days.

The Dow registered its worst point implosion in a single session in its more than 120-year history, warranting mainstream media attention. And 24 hours later, the Dow closed up 570 points, or 2.3%, while the S&P 500 booked a gain of 1.7% on Tuesday.

See also: What now? How to make sense of the stock market’s wild ride

What’s going on? After all, stocks had been winning so fast and so furiously in recent sessions it felt as though they might never return to Earth.

Although there is no specific reason for the sudden downturn and what appears to be a resurgence of choppy trade, market participants have cited a few factors that they say have contributed to this new regime of volatility and downdrafts. Here are a few:

Gravity

What goes up must come down. After a mostly relentless climb for stocks, both domestically and abroad, market pundits have been warning that stocks, which have been trading at lofty valuations, would ultimately revert lower at some point.

See also: Here are 3 key takeaways from the stock-market selloff

Inflation fears

Sluggish inflation had helped to stay the Federal Reserve’s desire to normalize interest rates from the period during the 2007-09 financial crisis. In theory, an era of ultralow interest rates have pushed investors into riskier assets and away from haven bonds, however, wages haven’t risen in step with the climb in the prices of stocks, despite a labor market that has been healthy, puzzling economists and Fed policy makers.

Signs of inflation rising at or above the Fed’s 2% annual target has sparked fears that inflation might re-emerge with a vengeance, rattling government paper, because they offer fixed payments and rising prices can eat away its value. Consequently, higher yields can translate into higher borrowing costs for corporations, potentially cooling their pace of growth.

Rising bond yields

Bonds had been on the rise lately. The 10-year Treasury note yield TMUBMUSD10Y, 0.701% hit a high on Monday at 2.88%, extending its climb to a fresh four-year peak for yields.

Government paper has been on the rise for two key reasons: the aforementioned rising inflation expectations and concerns that the Federal Reserve will be quicker to normalize interest-rate policy in the face of an economy that looked to be on solid footing.

Higher yields can compete with demand for stocks as investors weigh the risk and rewards of both assets.

An increase in borrowing costs can be digested by companies if corporate earnings improve in tandem with a rise in rates and if the economy holds steady.

Volatility, my old friend

A combination of valuation of rising yields, lofty equity valuations, inflation fears and anxieties about how far and fast the market had risen in a short period helped to foment volatility, which had been otherwise languid over the past two years.

See also: XIV trader: ‘I’ve lost $4 million, 3 years of work and other people’s money’

A pair of trades in particular that went decidedly sour, the VelocityShares Daily Inverse VIX Short Term ETN US:XIV and the ProShares Short VIX Short-Term Futures ETF SVXY, +0.05% , which represent exchange-traded products used to bet against rising volatility in the market, got buried when the index that they track, the Cboe Volatility Index VIX, -2.38% , saw its sharpest percentage rise in history, crushing investors, notably in XIV.

The demise of products like that is expected to stoke increased volatility in the market as short-volatility investors are forced to unwind their positions, which can fuel further swings in the market. Some of that action was seen on Tuesday as the Dow’s moves spanned 1,000 points in early trade, switching between sharp gains and losses:

Source: FactSet

Technical factors accelerated the trade

Trades like the volatility products contributed to the choppiness in the market and accelerated Monday’s wicked selloff. However, the S&P 500 index and the Dow slipping beneath their short-term, 50-day trading averages also triggered additional selling from computer-driven trades that are pegged to technical levels, note analysts at TS Lombard in a Tuesday research note (see excerpt below).