The most common causes of tsunamis are earthquakes that move the ocean floor. However large landslides can also cause tsunamis. The tallest tsunami ever recorded occurred due to a landslide in Alaska. The wave produced was 524 metres high! For reference, the maximum tsunami height after the 2011 earthquake in Japan was around 40 metres.
More information:
[1] http://geology.com/records/biggest-tsunami.shtml
CLIMATE AND GEOHAZARDS 