"What makes an investor risk averse?" and "What phenomena tend to raise implied vols?" are two different questions.
Typically a particular investor's level of risk aversion will vary at a much slower rate, based on their particular life circumstances. For example, their net worth, target net worth, living expenses, comfort with volatility, etc.
Theoretically, at this instant, you have a particular level of risk aversion. So, that level of risk aversion could cause you to bid up or down the price of an option based on your perspective of the risk inherit in a particular underlying asset at that time. Probably most of the time, you would believe some price is near an equilibrium, or within some tolerable level of that price, such that you would not engage in trading.
Realistically, it would require a collection of investors bidding up/down the price of options to see significant price movements which affect the implied volatility you're talking about. And basically what kind of events will cause a collection of investors to change their perspective of an underlying asset simultaneously? News is the most likely candidate to reach a large number of people at the same time. Could be any variety of news, earnings (as you mention), macroeconomic news, press releases about a firm, etc.