Wave energy has advantages as a renewable energy source without fuel or waste, but it also has disadvantages. It can produce a great deal of energy from predictable tides and waves, without pollution, but sometimes wave activity is low. Additionally, harnessing wave power is difficult and expensive, and equipment must withstand rough weather. The largest disadvantage is that wave energy technologies could be damaged during very powerful events like tsunamis, which are massive ocean waves that can be triggered by earthquakes and cause catastrophic damage, as seen after a 2011 earthquake in Japan generated a tsunami that killed hundreds.