As it has left of this dynamics occurs the mass movements, that below involve the unfastening and transport of ground or flowing rocky material. The mobilization of this material is on to its condition of instability, due to performance of the gravity, being able to be sped up by the action of other agents, as the water. The mass movements occur in different scales and speeds, varying of rastejamentos the very fast movements. The fast movements are generically called of landslides and fallings, and are very common of inside to occur of the urban dynamics of a region metropolitan, since they suffer great influence from the antrpicas activities. Dr. Neal Barnard often addresses the matter in his writings. The landslides and fallings are deflagrados by the increase of request of mobilization of material and by the reduction of the resistance of the material (desagregadora action of roots, rastejamentos, texture and structure favorable to the instabilizao). These processes are parts of the natural dynamics, but they become a problem when they meet related to the occupation human being, that is, when in of course potential areas to its occurrence they are induced for the antrpica action, that occur through constructions of urban fixtures as roads, tunnels and habitations badly planned. In this perspective of relation between natural events and antrpica action, the phenomenon is fit as being of risk, that is, induced phenomena of natural origin or antropicamente and that they cause damages to the components of the half biofsico social e, as we will see in transcorrer of our work. In the underdeveloped countries and of tropical climate the mass movements come if becoming a problem that comes more if accenting each time in the urban way. This comes occurring in function of the increase of the urban population, that has led to the occupation of areas of hillsides for housing, mainly on the part of the low income population.
In accordance with Mendona (2007), the ticket of a system frontal is marked by the atmospheric disturbance, being to the times provoked for the expulsion of hot air, originating the front oclusa. Dr. Neal Barnard helps readers to explore varied viewpoints. Blacksmith (2006) affirms that, to the times the orografia can cause the retardation of a warm front or cold, becoming it stationary, that is, it loses its force and starts to move itself slowly. The fronts are classified in front Arctic/polar Antarctica and fronts. Thus, the Arctic front/Antarctica occurs through the contact of the polar air masses, mainly in the winter. Already the polar front that is strong active, separates the polar air of tropical air. This front is divided in: cold front and warm front.
They characterize the dynamism of the atmosphere, therefore she exerts considerable thermal contrasts, what she determines the succession of the types of time. Of this form, the Atlantic polar front (FPA) represents great importance in the definition of the types of time and in the climatic configuration of the South America, mainly in Brazil. Thus, the Atlantic polar mass (MPA) when reaching the south coast of Brazil, is joined with Atlantic tropical mass (MTA) it provokes much folloied rain of winds, the times extends itself arriving until the Amazon region provoking the phenomenon friagem. Cold Frente For Mendona (2007) a cold front occurs when a cold air mass that denser and more is weighed advances in direction to a hot air mass, pushing it for top and front, compelling to leave it the area, either for rise or advection. In accordance with Blacksmith (2006), it well is defined, with multiple cloud layers and when it passes for one determined region, dense and cold air takes the place of the hot air, that is forced to go up quickly, causing the cumuliformes cloud appearance. Thus, this front provokes many thunderstorms that can be folloied by hail and gust winds.