A volcano may be labelled WATCH and ORANGE at the same time. These are not conflicting predictions. USGS separately describes a volcano's status for people and infrastructure on the ground and its implications for aviation. To understand a notice, identify the system being used, its publication date and the area covered by the guidance.
Identify the system and the catalogue's coverage
The national USGS system applies to volcanoes in the United States. Agencies in other countries may use different scales and procedures. The same colour in two systems need not mean the same condition. Compare the observatory's definitions rather than relying only on the appearance of an icon or the translation of a short label.
The app contains 170 entries from the USGS catalogue of US volcanoes. It is not a global volcano encyclopaedia or a complete eruption archive. A card helps you locate a volcano and find its latest available source notice. A foreign volcano missing from the app reflects the catalogue's coverage, not an absence of volcanic activity in that country.
The four ground alert levels describe conditions
NORMAL describes a typical non-eruptive background state. ADVISORY indicates activity above the known background, or a substantial decrease from a higher level with continued monitoring. Background activity can include steam, gas emissions and small earthquakes: NORMAL does not require a completely motionless volcano.
WATCH applies to heightened or escalating unrest with increased eruption potential and uncertain timing, or an eruption already under way with limited hazards. WARNING means a hazardous eruption is imminent, occurring or suspected. The categories communicate an assessment of conditions, not a timetable stating exactly when an eruption will begin or end.
Aviation colours address ash in the atmosphere
GREEN and YELLOW indicate background conditions and elevated unrest respectively. ORANGE can accompany escalating unrest or an eruption with little or no ash. RED concerns significant ash emissions that are likely to occur imminently, occurring or suspected. Volcanic ash consists of small fragments of rock and glass, and wind can carry it far from a summit.
The ground and aviation assessments can diverge. Dangerous lava flows need not produce a substantial ash plume, while ash can affect flight routes when local ground impacts are limited. UNASSIGNED is used when ground-based instrumentation is insufficient to establish background conditions. It must not be interpreted as an extra category of safety.
Read the whole notice
USGS issues a Volcano Activity Notice, or VAN, when a ground alert level changes, and a Volcano Observatory Notice for Aviation, or VONA, for changes in the aviation code. The explanation matters alongside the new label. Observations of seismicity, deformation, gas or ash supply context that a short headline inevitably leaves out.
Check the date of the latest available notice on the card and open the original. A saved notice still describes conditions at its stated time, even when you can open the screen offline. A missing recent record may indicate a retrieval problem. It establishes neither that activity has stopped nor that access restrictions have been removed.
- Which agency issued the notice, and which volcano does it concern?
- When was it published, and which level changed?
- What phenomena are being observed, and where do restrictions apply?
Travel decisions need local information
An activity level does not replace a hazard map. Lahars can travel down valleys far from a summit, and wind determines where ash is carried. Two places at the same distance from a crater can face different conditions. A circle on a map and a volcano's elevation cannot establish a safe hiking route or campsite.
Before visiting, check the local authorities, observatory and land manager for closed areas, exit routes and official information channels. Follow evacuation instructions when issued. The app's lessons and volcano model help explain processes; they do not calculate the routes of lava, ash or lahars for your trip.
FAQ
Does NORMAL mean I can walk to the crater?
No. It describes background conditions in the USGS system and is not an access permit. Gas, unstable ground, hydrothermal activity and local rules may restrict visits at any alert level.
Why can a volcano have WARNING and ORANGE rather than RED?
Ground alert levels and aviation colours address different aspects of the activity. A hazardous eruption with substantial lava flows, for example, may produce little ash. Read the official notice for the explanation.
Sources
This is educational information. For emergency decisions, follow local authorities and official warnings.
