Because all forces are created by major forces, major forces are the biggest forces, and cannot be exceeded in any direction by minor forces or components. Whenever a major force is transmitted through a surface, the component of the force that is at a right angle to the surface becomes a minor force. Any reaction from that force then has to be calculated from the minor force, as that is the actual physical force that would be present. Using Newton’s 3rd law, every force has an equal and opposite reaction, so any force transmitted from a surface to another surface will have an even force transmitted back. This is the reaction force, and is the force of which its components can change our velocity. Expert heliskiing

So as an example to see how the forces between a ski and the snow act in different directions, we are going to look at a ski that is sitting at an angle to the slope along 2 different axis. Below is an explanation of how the forces are calculated:

For this calculation to be done effectively, we need to take note of the angle at which the ski is sitting on the slope lengthwise and also of the angle at which the ski is sitting on the slope sideways. The only major force which should be acting on the ski should be gravity. The first thing that is calculated is the component of gravity which is at the same angle as the slope along the skis length. Next, this force is equaled in the opposite direction by a reaction from the slope and then a vertical component is calculated. Once this is done, you must figure out what the minor component for the force is in the sideways direction. The amount of force that you discover from this operation is usually referred to as the force of the z-y plane. Extreme heliskiing  
 

From this force we can also work out the force in the x-y plane as the vertical component will be the same. So we calculate the vertical component and then from that we can work out the actual reaction component from the slope in the x-y plane. We can also calculate the sideways components of the reaction force. To work out the actual reaction force that the slope pushes back with at a right angle to its surface, we then take the x, y and z components, and put them together using Pythagoras. Once you have done this, you will have an accurate representation of the amount of reaction force which your skis will experience out on the slopes.