There are a range in style of eruptions from effusive to explosive. 

1. Icelandic: These are lava flows orginating from fissure, or long cracks, along the Earth's surface. Instead of creating hills and/or mountains, they will create lava plateaus.
2. Hawaiian: Similar to Iceland these erup[tions orginate from sheild volcanoes. These sheilds are gantle sloping hills and mountains where lava flows and erupts in lava fountains from vents in the ground centered in these sheilds. 
3. Strombolian eruptions are more explosive, but tend to be less destructive. Cindercones eject lava, gas, and ash in pulsing bursts caused by gas build-up in the vent.
4. Vulcanian eruptions are more powerful and are where we start to see eruption columns (or ash clouds) start to form. These plumes of ash  tend to be around 10 km (6 miles) high. Ejections from vulcanian eruptions include ash, gas, and larger fragments known as bombs, and can sometimes include smaller lava flows as well. 
5. Pelean eruptions are known for their pyroclastic flows. While there can sometimes be small amounts of lava flows from these eruptions it is much less common.
6. The last syle, Plinian is the most explosive and the most destructive. These are poweful, sustained eupruptions from composite volcanoes (stratovolcanoes). Plinians are known for their towerin eruption columns that can reach over 40 km (25 mi) high. The hazards associated with these are wide-spread ash fall, pyroclastic flows, and lahars. 

It is important to know the different hazard that can come from volcanic activity and eruptions, especially when planning to travel and vist. 

• Lava: Lava ranges in termperature form 700-1,200C (1,300-2,200F). How quickly it flows will depend on it's viscosity. Lower viscosity will be much quicker, and while higher viscosity is slower there will are possibility of gas bubbles that can burt and cuase the lava to splash suddenly. Keeping a safe distance is alwas recommended.
• Ash: It is important to remember this is not like ash from a campfire. Ash erupted from a volcano is rock. It's more dense and abrasive. Inhaling too much can cause it to mix with the moisture in your lungs creating a liquid-like cement. Keep your nose and mouth covered. It can also take as little as 10 cm of ash to collapse a roof.
• Gas: There are many gases that can be emitted from a volcano. This is dangerous as it is not necessarily known when gas is being released. If you are hiking a volcano and you feel any sudden dizziness, nausea, light headedness, or extreme heat. Retreat back to where you came from immediately. 
• Pyroclastic Flow: These are super heated clouds of rock and ash that flow down the slopes of the volcano. These are caused when a portion of the dome is blown out or collapses. Flows can tavel up to 100 km (60 miles) per hour and rang in temperature form 600-700C (1,100-1,300F).
• Lahar: Lahars are debris flows caused when the glaciers atop the volcano suddenly melt causing water, rock, ash, and anything else caught up in it to rush down the side of the mountian. These will normally follow drainage paths so getting to higher ground is best. 

The volcanic explosivity index (VEI) is a way to catergorize and measure the scale of explosiveness of an eruptuion. This is a function of force and the volume of material erupted ranginf from 0-8. Becasue of this it's not only based on explosivity, however for simplicity I have classified it as such:

• VEI 0: Effusive eruptions, like Hawaiian and Icelandic
• VEI 1-2: Strombolian
• VEI 3-4: Volcanian and Pelean
• VEI 5-7: Plinian
• VEI 8: Supereruptions
  • Important note- volcanoes capable of a super eruption are also capable of smaller eruptions with lower VEIs. Increased activty at these volcanoes does not automatically mean supereruption. 

If you would like to know what volcanoes are at risk here are some links:

USGS: Volcano Updates | U.S. Geological Survey

Global Volcanism Program: Smithsonian Institution - Global Volcanism Program: Worldwide Holocene Volcano and Eruption Information

Italy: Volcanoes in Italy - Volcanic risk | Dipartimento della Protezione Civile

Japan: Japan Meteorological Agency｜Volcanic Warnings

Philippines: Volcanoes of the Philippines