Final answer:
True statements about landslides and tsunamis include that landslides are caused by downslope movement of earth materials, tsunamis are large waves generated by geological events, and both can cause serious environmental and human damage. Incorrect statements include that they cannot be prevented and are solely caused by human activities.
Step-by-step explanation:
Among the true statements about landslides and tsunamis are:
Landslides are caused by the movement of rocks and soil down a slope.
Tsunamis are large ocean waves caused by underwater earthquakes or volcanic eruptions.
Landslides and tsunamis can both cause significant damage to the environment and human settlements.
However, not all of the provided statements are correct. While both landslides and tsunamis are natural disasters, it is incorrect to say they cannot be prevented. Through geological investigations, good engineering practices, and land-use regulations, the risks associated with landslides can be reduced. Moreover, while human activities can sometimes trigger these events, it is not correct to attribute the cause of landslides and tsunamis solely to human actions, as they are often the result of natural processes such as earthquakes, volcanoes, and the movement of tectonic plates.
As for tsunamis, their properties in deep and shallow water differ significantly. When travelling over deep ocean, a tsunami's height may be less than 30 cm, and it can speed across the ocean at up to 700 km/hr. However, as it reaches shallow coastal waters, the wave slows down, and the sea level can rise dramatically, potentially up to 30 m. With wave periods as long as an hour and wavelengths extending to 100 km, tsunamis can travel great distances, causing widespread destruction upon reaching the shore.